author | Nishanth Amuluru <nishanth@fossee.in> |
Sat, 08 Jan 2011 20:25:05 +0530 | |
changeset 319 | 70726699ca80 |
parent 307 | c6bca38c1cbf |
permissions | -rw-r--r-- |
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1 |
================================ |
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Custom template tags and filters |
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================================ |
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Introduction |
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============ |
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Django's template system comes with a wide variety of :doc:`built-in |
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tags and filters </ref/templates/builtins>` designed to address the |
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presentation logic needs of your application. Nevertheless, you may |
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find yourself needing functionality that is not covered by the core |
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set of template primitives. You can extend the template engine by |
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defining custom tags and filters using Python, and then make them |
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available to your templates using the ``{% load %}`` tag. |
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|
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Code layout |
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----------- |
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Custom template tags and filters must live inside a Django app. If they relate |
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to an existing app it makes sense to bundle them there; otherwise, you should |
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create a new app to hold them. |
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|
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The app should contain a ``templatetags`` directory, at the same level as |
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``models.py``, ``views.py``, etc. If this doesn't already exist, create it - |
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don't forget the ``__init__.py`` file to ensure the directory is treated as a |
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Python package. |
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Your custom tags and filters will live in a module inside the ``templatetags`` |
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directory. The name of the module file is the name you'll use to load the tags |
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later, so be careful to pick a name that won't clash with custom tags and |
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filters in another app. |
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For example, if your custom tags/filters are in a file called |
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``poll_extras.py``, your app layout might look like this:: |
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polls/ |
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models.py |
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templatetags/ |
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__init__.py |
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poll_extras.py |
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views.py |
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And in your template you would use the following: |
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.. code-block:: html+django |
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{% load poll_extras %} |
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The app that contains the custom tags must be in :setting:`INSTALLED_APPS` in |
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order for the ``{% load %}`` tag to work. This is a security feature: It allows |
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you to host Python code for many template libraries on a single host machine |
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without enabling access to all of them for every Django installation. |
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There's no limit on how many modules you put in the ``templatetags`` package. |
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Just keep in mind that a ``{% load %}`` statement will load tags/filters for |
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the given Python module name, not the name of the app. |
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To be a valid tag library, the module must contain a module-level variable |
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named ``register`` that is a ``template.Library`` instance, in which all the |
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tags and filters are registered. So, near the top of your module, put the |
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following:: |
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from django import template |
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register = template.Library() |
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.. admonition:: Behind the scenes |
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For a ton of examples, read the source code for Django's default filters |
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and tags. They're in ``django/template/defaultfilters.py`` and |
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``django/template/defaulttags.py``, respectively. |
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Writing custom template filters |
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------------------------------- |
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Custom filters are just Python functions that take one or two arguments: |
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* The value of the variable (input) -- not necessarily a string. |
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* The value of the argument -- this can have a default value, or be left |
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out altogether. |
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For example, in the filter ``{{ var|foo:"bar" }}``, the filter ``foo`` would be |
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passed the variable ``var`` and the argument ``"bar"``. |
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Filter functions should always return something. They shouldn't raise |
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exceptions. They should fail silently. In case of error, they should return |
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either the original input or an empty string -- whichever makes more sense. |
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Here's an example filter definition:: |
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def cut(value, arg): |
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"Removes all values of arg from the given string" |
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return value.replace(arg, '') |
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And here's an example of how that filter would be used: |
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.. code-block:: html+django |
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{{ somevariable|cut:"0" }} |
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Most filters don't take arguments. In this case, just leave the argument out of |
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your function. Example:: |
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def lower(value): # Only one argument. |
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"Converts a string into all lowercase" |
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return value.lower() |
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Template filters that expect strings |
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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If you're writing a template filter that only expects a string as the first |
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argument, you should use the decorator ``stringfilter``. This will |
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convert an object to its string value before being passed to your function:: |
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from django.template.defaultfilters import stringfilter |
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@stringfilter |
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def lower(value): |
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return value.lower() |
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120 |
|
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This way, you'll be able to pass, say, an integer to this filter, and it |
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won't cause an ``AttributeError`` (because integers don't have ``lower()`` |
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123 |
methods). |
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124 |
|
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125 |
Registering custom filters |
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126 |
~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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127 |
|
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128 |
Once you've written your filter definition, you need to register it with |
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129 |
your ``Library`` instance, to make it available to Django's template language:: |
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130 |
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131 |
register.filter('cut', cut) |
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132 |
register.filter('lower', lower) |
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133 |
|
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134 |
The ``Library.filter()`` method takes two arguments: |
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135 |
|
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136 |
1. The name of the filter -- a string. |
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137 |
2. The compilation function -- a Python function (not the name of the |
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138 |
function as a string). |
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139 |
|
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140 |
You can use ``register.filter()`` as a decorator instead:: |
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141 |
|
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142 |
@register.filter(name='cut') |
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143 |
@stringfilter |
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144 |
def cut(value, arg): |
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return value.replace(arg, '') |
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146 |
|
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147 |
@register.filter |
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148 |
@stringfilter |
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149 |
def lower(value): |
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150 |
return value.lower() |
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151 |
|
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152 |
If you leave off the ``name`` argument, as in the second example above, Django |
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153 |
will use the function's name as the filter name. |
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154 |
|
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155 |
Filters and auto-escaping |
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156 |
~~~~~~~~~~~~~~~~~~~~~~~~~ |
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157 |
|
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158 |
.. versionadded:: 1.0 |
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159 |
|
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160 |
When writing a custom filter, give some thought to how the filter will interact |
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161 |
with Django's auto-escaping behavior. Note that three types of strings can be |
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162 |
passed around inside the template code: |
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163 |
|
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164 |
* **Raw strings** are the native Python ``str`` or ``unicode`` types. On |
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165 |
output, they're escaped if auto-escaping is in effect and presented |
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166 |
unchanged, otherwise. |
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167 |
|
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168 |
* **Safe strings** are strings that have been marked safe from further |
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169 |
escaping at output time. Any necessary escaping has already been done. |
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170 |
They're commonly used for output that contains raw HTML that is intended |
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171 |
to be interpreted as-is on the client side. |
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172 |
|
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173 |
Internally, these strings are of type ``SafeString`` or ``SafeUnicode``. |
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174 |
They share a common base class of ``SafeData``, so you can test |
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175 |
for them using code like:: |
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176 |
|
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177 |
if isinstance(value, SafeData): |
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178 |
# Do something with the "safe" string. |
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179 |
|
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180 |
* **Strings marked as "needing escaping"** are *always* escaped on |
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181 |
output, regardless of whether they are in an ``autoescape`` block or not. |
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182 |
These strings are only escaped once, however, even if auto-escaping |
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183 |
applies. |
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184 |
|
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185 |
Internally, these strings are of type ``EscapeString`` or |
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186 |
``EscapeUnicode``. Generally you don't have to worry about these; they |
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187 |
exist for the implementation of the ``escape`` filter. |
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188 |
|
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189 |
Template filter code falls into one of two situations: |
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190 |
|
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191 |
1. Your filter does not introduce any HTML-unsafe characters (``<``, ``>``, |
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192 |
``'``, ``"`` or ``&``) into the result that were not already present. In |
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193 |
this case, you can let Django take care of all the auto-escaping |
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194 |
handling for you. All you need to do is put the ``is_safe`` attribute on |
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195 |
your filter function and set it to ``True``, like so:: |
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196 |
|
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197 |
@register.filter |
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198 |
def myfilter(value): |
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199 |
return value |
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200 |
myfilter.is_safe = True |
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201 |
|
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202 |
This attribute tells Django that if a "safe" string is passed into your |
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203 |
filter, the result will still be "safe" and if a non-safe string is |
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204 |
passed in, Django will automatically escape it, if necessary. |
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205 |
|
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206 |
You can think of this as meaning "this filter is safe -- it doesn't |
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207 |
introduce any possibility of unsafe HTML." |
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208 |
|
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209 |
The reason ``is_safe`` is necessary is because there are plenty of |
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210 |
normal string operations that will turn a ``SafeData`` object back into |
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211 |
a normal ``str`` or ``unicode`` object and, rather than try to catch |
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212 |
them all, which would be very difficult, Django repairs the damage after |
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213 |
the filter has completed. |
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214 |
|
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215 |
For example, suppose you have a filter that adds the string ``xx`` to the |
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216 |
end of any input. Since this introduces no dangerous HTML characters to |
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217 |
the result (aside from any that were already present), you should mark |
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218 |
your filter with ``is_safe``:: |
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219 |
|
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220 |
@register.filter |
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221 |
def add_xx(value): |
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222 |
return '%sxx' % value |
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223 |
add_xx.is_safe = True |
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224 |
|
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225 |
When this filter is used in a template where auto-escaping is enabled, |
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226 |
Django will escape the output whenever the input is not already marked as |
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227 |
"safe". |
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228 |
|
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229 |
By default, ``is_safe`` defaults to ``False``, and you can omit it from |
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230 |
any filters where it isn't required. |
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231 |
|
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232 |
Be careful when deciding if your filter really does leave safe strings |
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233 |
as safe. If you're *removing* characters, you might inadvertently leave |
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234 |
unbalanced HTML tags or entities in the result. For example, removing a |
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235 |
``>`` from the input might turn ``<a>`` into ``<a``, which would need to |
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be escaped on output to avoid causing problems. Similarly, removing a |
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semicolon (``;``) can turn ``&`` into ``&``, which is no longer a |
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valid entity and thus needs further escaping. Most cases won't be nearly |
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this tricky, but keep an eye out for any problems like that when |
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reviewing your code. |
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|
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Marking a filter ``is_safe`` will coerce the filter's return value to |
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a string. If your filter should return a boolean or other non-string |
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value, marking it ``is_safe`` will probably have unintended |
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consequences (such as converting a boolean False to the string |
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'False'). |
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|
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2. Alternatively, your filter code can manually take care of any necessary |
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escaping. This is necessary when you're introducing new HTML markup into |
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the result. You want to mark the output as safe from further |
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escaping so that your HTML markup isn't escaped further, so you'll need |
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to handle the input yourself. |
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|
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To mark the output as a safe string, use |
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:func:`django.utils.safestring.mark_safe`. |
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|
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Be careful, though. You need to do more than just mark the output as |
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safe. You need to ensure it really *is* safe, and what you do depends on |
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whether auto-escaping is in effect. The idea is to write filters than |
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can operate in templates where auto-escaping is either on or off in |
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order to make things easier for your template authors. |
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|
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In order for your filter to know the current auto-escaping state, set |
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the ``needs_autoescape`` attribute to ``True`` on your function. (If you |
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don't specify this attribute, it defaults to ``False``). This attribute |
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tells Django that your filter function wants to be passed an extra |
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keyword argument, called ``autoescape``, that is ``True`` if |
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auto-escaping is in effect and ``False`` otherwise. |
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|
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For example, let's write a filter that emphasizes the first character of |
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a string:: |
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|
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from django.utils.html import conditional_escape |
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from django.utils.safestring import mark_safe |
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|
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def initial_letter_filter(text, autoescape=None): |
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first, other = text[0], text[1:] |
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if autoescape: |
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esc = conditional_escape |
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else: |
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esc = lambda x: x |
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result = '<strong>%s</strong>%s' % (esc(first), esc(other)) |
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return mark_safe(result) |
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initial_letter_filter.needs_autoescape = True |
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285 |
|
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The ``needs_autoescape`` attribute on the filter function and the |
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``autoescape`` keyword argument mean that our function will know whether |
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automatic escaping is in effect when the filter is called. We use |
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``autoescape`` to decide whether the input data needs to be passed |
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through ``django.utils.html.conditional_escape`` or not. (In the latter |
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case, we just use the identity function as the "escape" function.) The |
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``conditional_escape()`` function is like ``escape()`` except it only |
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escapes input that is **not** a ``SafeData`` instance. If a ``SafeData`` |
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instance is passed to ``conditional_escape()``, the data is returned |
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unchanged. |
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296 |
|
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Finally, in the above example, we remember to mark the result as safe |
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so that our HTML is inserted directly into the template without further |
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escaping. |
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300 |
|
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There's no need to worry about the ``is_safe`` attribute in this case |
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(although including it wouldn't hurt anything). Whenever you manually |
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303 |
handle the auto-escaping issues and return a safe string, the |
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``is_safe`` attribute won't change anything either way. |
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305 |
|
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306 |
Writing custom template tags |
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307 |
---------------------------- |
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308 |
|
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Tags are more complex than filters, because tags can do anything. |
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310 |
|
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311 |
A quick overview |
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312 |
~~~~~~~~~~~~~~~~ |
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313 |
|
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314 |
Above, this document explained that the template system works in a two-step |
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process: compiling and rendering. To define a custom template tag, you specify |
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316 |
how the compilation works and how the rendering works. |
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317 |
|
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318 |
When Django compiles a template, it splits the raw template text into |
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''nodes''. Each node is an instance of ``django.template.Node`` and has |
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a ``render()`` method. A compiled template is, simply, a list of ``Node`` |
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objects. When you call ``render()`` on a compiled template object, the template |
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calls ``render()`` on each ``Node`` in its node list, with the given context. |
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The results are all concatenated together to form the output of the template. |
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324 |
|
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Thus, to define a custom template tag, you specify how the raw template tag is |
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converted into a ``Node`` (the compilation function), and what the node's |
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327 |
``render()`` method does. |
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328 |
|
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329 |
Writing the compilation function |
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330 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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331 |
|
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332 |
For each template tag the template parser encounters, it calls a Python |
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333 |
function with the tag contents and the parser object itself. This function is |
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334 |
responsible for returning a ``Node`` instance based on the contents of the tag. |
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335 |
|
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336 |
For example, let's write a template tag, ``{% current_time %}``, that displays |
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the current date/time, formatted according to a parameter given in the tag, in |
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`strftime syntax`_. It's a good idea to decide the tag syntax before anything |
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else. In our case, let's say the tag should be used like this: |
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340 |
|
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341 |
.. code-block:: html+django |
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342 |
|
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<p>The time is {% current_time "%Y-%m-%d %I:%M %p" %}.</p> |
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|
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.. _`strftime syntax`: http://docs.python.org/library/time.html#time.strftime |
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|
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The parser for this function should grab the parameter and create a ``Node`` |
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object:: |
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349 |
|
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350 |
from django import template |
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351 |
def do_current_time(parser, token): |
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352 |
try: |
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353 |
# split_contents() knows not to split quoted strings. |
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354 |
tag_name, format_string = token.split_contents() |
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355 |
except ValueError: |
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356 |
raise template.TemplateSyntaxError, "%r tag requires a single argument" % token.contents.split()[0] |
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357 |
if not (format_string[0] == format_string[-1] and format_string[0] in ('"', "'")): |
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358 |
raise template.TemplateSyntaxError, "%r tag's argument should be in quotes" % tag_name |
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359 |
return CurrentTimeNode(format_string[1:-1]) |
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360 |
|
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|
361 |
Notes: |
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362 |
|
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363 |
* ``parser`` is the template parser object. We don't need it in this |
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|
364 |
example. |
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365 |
|
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366 |
* ``token.contents`` is a string of the raw contents of the tag. In our |
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367 |
example, it's ``'current_time "%Y-%m-%d %I:%M %p"'``. |
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368 |
|
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369 |
* The ``token.split_contents()`` method separates the arguments on spaces |
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370 |
while keeping quoted strings together. The more straightforward |
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371 |
``token.contents.split()`` wouldn't be as robust, as it would naively |
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372 |
split on *all* spaces, including those within quoted strings. It's a good |
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373 |
idea to always use ``token.split_contents()``. |
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|
374 |
|
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375 |
* This function is responsible for raising |
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376 |
``django.template.TemplateSyntaxError``, with helpful messages, for |
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377 |
any syntax error. |
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378 |
|
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379 |
* The ``TemplateSyntaxError`` exceptions use the ``tag_name`` variable. |
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|
380 |
Don't hard-code the tag's name in your error messages, because that |
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381 |
couples the tag's name to your function. ``token.contents.split()[0]`` |
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382 |
will ''always'' be the name of your tag -- even when the tag has no |
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383 |
arguments. |
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|
384 |
|
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385 |
* The function returns a ``CurrentTimeNode`` with everything the node needs |
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|
386 |
to know about this tag. In this case, it just passes the argument -- |
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|
387 |
``"%Y-%m-%d %I:%M %p"``. The leading and trailing quotes from the |
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|
388 |
template tag are removed in ``format_string[1:-1]``. |
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|
389 |
|
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|
390 |
* The parsing is very low-level. The Django developers have experimented |
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|
391 |
with writing small frameworks on top of this parsing system, using |
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|
392 |
techniques such as EBNF grammars, but those experiments made the template |
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|
393 |
engine too slow. It's low-level because that's fastest. |
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|
394 |
|
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|
395 |
Writing the renderer |
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|
396 |
~~~~~~~~~~~~~~~~~~~~ |
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|
397 |
|
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|
398 |
The second step in writing custom tags is to define a ``Node`` subclass that |
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|
399 |
has a ``render()`` method. |
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|
400 |
|
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|
401 |
Continuing the above example, we need to define ``CurrentTimeNode``:: |
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|
402 |
|
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|
403 |
from django import template |
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|
404 |
import datetime |
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|
405 |
class CurrentTimeNode(template.Node): |
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406 |
def __init__(self, format_string): |
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407 |
self.format_string = format_string |
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|
408 |
def render(self, context): |
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|
409 |
return datetime.datetime.now().strftime(self.format_string) |
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|
410 |
|
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|
411 |
Notes: |
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|
412 |
|
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|
413 |
* ``__init__()`` gets the ``format_string`` from ``do_current_time()``. |
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|
414 |
Always pass any options/parameters/arguments to a ``Node`` via its |
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|
415 |
``__init__()``. |
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|
416 |
|
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|
417 |
* The ``render()`` method is where the work actually happens. |
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|
418 |
|
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|
419 |
* ``render()`` should never raise ``TemplateSyntaxError`` or any other |
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Added buildout stuff and made changes accordingly
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|
420 |
exception. It should fail silently, just as template filters should. |
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|
421 |
|
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|
422 |
Ultimately, this decoupling of compilation and rendering results in an |
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|
423 |
efficient template system, because a template can render multiple contexts |
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Added buildout stuff and made changes accordingly
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|
424 |
without having to be parsed multiple times. |
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|
425 |
|
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|
426 |
Auto-escaping considerations |
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|
427 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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|
428 |
|
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|
429 |
.. versionadded:: 1.0 |
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|
430 |
|
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|
431 |
The output from template tags is **not** automatically run through the |
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|
432 |
auto-escaping filters. However, there are still a couple of things you should |
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|
433 |
keep in mind when writing a template tag. |
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|
434 |
|
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Added buildout stuff and made changes accordingly
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|
435 |
If the ``render()`` function of your template stores the result in a context |
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Added buildout stuff and made changes accordingly
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|
436 |
variable (rather than returning the result in a string), it should take care |
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Added buildout stuff and made changes accordingly
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|
437 |
to call ``mark_safe()`` if appropriate. When the variable is ultimately |
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Added buildout stuff and made changes accordingly
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|
438 |
rendered, it will be affected by the auto-escape setting in effect at the |
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Added buildout stuff and made changes accordingly
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|
439 |
time, so content that should be safe from further escaping needs to be marked |
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|
440 |
as such. |
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Added buildout stuff and made changes accordingly
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|
441 |
|
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|
442 |
Also, if your template tag creates a new context for performing some |
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Added buildout stuff and made changes accordingly
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|
443 |
sub-rendering, set the auto-escape attribute to the current context's value. |
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Added buildout stuff and made changes accordingly
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|
444 |
The ``__init__`` method for the ``Context`` class takes a parameter called |
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|
445 |
``autoescape`` that you can use for this purpose. For example:: |
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|
446 |
|
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|
447 |
def render(self, context): |
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|
448 |
# ... |
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|
449 |
new_context = Context({'var': obj}, autoescape=context.autoescape) |
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|
450 |
# ... Do something with new_context ... |
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|
451 |
|
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|
452 |
This is not a very common situation, but it's useful if you're rendering a |
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Added buildout stuff and made changes accordingly
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|
453 |
template yourself. For example:: |
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|
454 |
|
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|
455 |
def render(self, context): |
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|
456 |
t = template.loader.get_template('small_fragment.html') |
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|
457 |
return t.render(Context({'var': obj}, autoescape=context.autoescape)) |
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|
458 |
|
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|
459 |
If we had neglected to pass in the current ``context.autoescape`` value to our |
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Added buildout stuff and made changes accordingly
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|
460 |
new ``Context`` in this example, the results would have *always* been |
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|
461 |
automatically escaped, which may not be the desired behavior if the template |
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|
462 |
tag is used inside a ``{% autoescape off %}`` block. |
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|
463 |
|
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|
464 |
.. _template_tag_thread_safety: |
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|
465 |
|
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|
466 |
Thread-safety considerations |
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changeset
|
467 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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Nishanth Amuluru <nishanth@fossee.in>
parents:
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|
468 |
|
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Nishanth Amuluru <nishanth@fossee.in>
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|
469 |
.. versionadded:: 1.2 |
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Nishanth Amuluru <nishanth@fossee.in>
parents:
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changeset
|
470 |
|
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
471 |
Once a node is parsed, its ``render`` method may be called any number of times. |
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Added buildout stuff and made changes accordingly
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|
472 |
Since Django is sometimes run in multi-threaded environments, a single node may |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
473 |
be simultaneously rendering with different contexts in response to two separate |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
474 |
requests. Therefore, it's important to make sure your template tags are thread |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
475 |
safe. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
476 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
477 |
To make sure your template tags are thread safe, you should never store state |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
478 |
information on the node itself. For example, Django provides a builtin ``cycle`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
479 |
template tag that cycles among a list of given strings each time it's rendered:: |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
480 |
|
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
481 |
{% for o in some_list %} |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
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|
482 |
<tr class="{% cycle 'row1' 'row2' %}> |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
483 |
... |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
484 |
</tr> |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
485 |
{% endfor %} |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
486 |
|
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
487 |
A naive implementation of ``CycleNode`` might look something like this:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
488 |
|
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
489 |
class CycleNode(Node): |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
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|
490 |
def __init__(self, cyclevars): |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
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|
491 |
self.cycle_iter = itertools.cycle(cyclevars) |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
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|
492 |
def render(self, context): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
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|
493 |
return self.cycle_iter.next() |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
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|
494 |
|
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
495 |
But, suppose we have two templates rendering the template snippet from above at |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
496 |
the same time: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
497 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
498 |
1. Thread 1 performs its first loop iteration, ``CycleNode.render()`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
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|
499 |
returns 'row1' |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
500 |
2. Thread 2 performs its first loop iteration, ``CycleNode.render()`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
501 |
returns 'row2' |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
502 |
3. Thread 1 performs its second loop iteration, ``CycleNode.render()`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
503 |
returns 'row1' |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
504 |
4. Thread 2 performs its second loop iteration, ``CycleNode.render()`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
505 |
returns 'row2' |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
506 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
507 |
The CycleNode is iterating, but it's iterating globally. As far as Thread 1 |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
508 |
and Thread 2 are concerned, it's always returning the same value. This is |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
509 |
obviously not what we want! |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
510 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
511 |
To address this problem, Django provides a ``render_context`` that's associated |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
512 |
with the ``context`` of the template that is currently being rendered. The |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
513 |
``render_context`` behaves like a Python dictionary, and should be used to store |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
514 |
``Node`` state between invocations of the ``render`` method. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
515 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
516 |
Let's refactor our ``CycleNode`` implementation to use the ``render_context``:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
517 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
518 |
class CycleNode(Node): |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
519 |
def __init__(self, cyclevars): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
520 |
self.cyclevars = cyclevars |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
521 |
def render(self, context): |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
522 |
if self not in context.render_context: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
523 |
context.render_context[self] = itertools.cycle(self.cyclevars) |
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
524 |
cycle_iter = context.render_context[self] |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
525 |
return cycle_iter.next() |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
526 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
527 |
Note that it's perfectly safe to store global information that will not change |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
528 |
throughout the life of the ``Node`` as an attribute. In the case of |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
529 |
``CycleNode``, the ``cyclevars`` argument doesn't change after the ``Node`` is |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
530 |
instantiated, so we don't need to put it in the ``render_context``. But state |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
531 |
information that is specific to the template that is currently being rendered, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
532 |
like the current iteration of the ``CycleNode``, should be stored in the |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
533 |
``render_context``. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
534 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
535 |
.. note:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
536 |
Notice how we used ``self`` to scope the ``CycleNode`` specific information |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
537 |
within the ``render_context``. There may be multiple ``CycleNodes`` in a |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
538 |
given template, so we need to be careful not to clobber another node's state |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
539 |
information. The easiest way to do this is to always use ``self`` as the key |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
540 |
into ``render_context``. If you're keeping track of several state variables, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
541 |
make ``render_context[self]`` a dictionary. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
542 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
543 |
Registering the tag |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
544 |
~~~~~~~~~~~~~~~~~~~ |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
545 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
546 |
Finally, register the tag with your module's ``Library`` instance, as explained |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
547 |
in "Writing custom template filters" above. Example:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
548 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
549 |
register.tag('current_time', do_current_time) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
550 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
551 |
The ``tag()`` method takes two arguments: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
552 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
553 |
1. The name of the template tag -- a string. If this is left out, the |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
554 |
name of the compilation function will be used. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
555 |
2. The compilation function -- a Python function (not the name of the |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
556 |
function as a string). |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
557 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
558 |
As with filter registration, it is also possible to use this as a decorator:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
559 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
560 |
@register.tag(name="current_time") |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
561 |
def do_current_time(parser, token): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
562 |
# ... |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
563 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
564 |
@register.tag |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
565 |
def shout(parser, token): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
566 |
# ... |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
567 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
568 |
If you leave off the ``name`` argument, as in the second example above, Django |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
569 |
will use the function's name as the tag name. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
570 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
571 |
Passing template variables to the tag |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
572 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
573 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
574 |
Although you can pass any number of arguments to a template tag using |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
575 |
``token.split_contents()``, the arguments are all unpacked as |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
576 |
string literals. A little more work is required in order to pass dynamic |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
577 |
content (a template variable) to a template tag as an argument. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
578 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
579 |
While the previous examples have formatted the current time into a string and |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
580 |
returned the string, suppose you wanted to pass in a ``DateTimeField`` from an |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
581 |
object and have the template tag format that date-time: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
582 |
|
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Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
583 |
.. code-block:: html+django |
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584 |
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585 |
<p>This post was last updated at {% format_time blog_entry.date_updated "%Y-%m-%d %I:%M %p" %}.</p> |
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586 |
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587 |
Initially, ``token.split_contents()`` will return three values: |
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588 |
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589 |
1. The tag name ``format_time``. |
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590 |
2. The string "blog_entry.date_updated" (without the surrounding quotes). |
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591 |
3. The formatting string "%Y-%m-%d %I:%M %p". The return value from |
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592 |
``split_contents()`` will include the leading and trailing quotes for |
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593 |
string literals like this. |
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594 |
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595 |
Now your tag should begin to look like this:: |
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596 |
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597 |
from django import template |
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598 |
def do_format_time(parser, token): |
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599 |
try: |
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600 |
# split_contents() knows not to split quoted strings. |
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601 |
tag_name, date_to_be_formatted, format_string = token.split_contents() |
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602 |
except ValueError: |
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603 |
raise template.TemplateSyntaxError, "%r tag requires exactly two arguments" % token.contents.split()[0] |
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604 |
if not (format_string[0] == format_string[-1] and format_string[0] in ('"', "'")): |
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605 |
raise template.TemplateSyntaxError, "%r tag's argument should be in quotes" % tag_name |
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606 |
return FormatTimeNode(date_to_be_formatted, format_string[1:-1]) |
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607 |
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608 |
.. versionchanged:: 1.0 |
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609 |
Variable resolution has changed in the 1.0 release of Django. ``template.resolve_variable()`` |
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610 |
has been deprecated in favor of a new ``template.Variable`` class. |
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611 |
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612 |
You also have to change the renderer to retrieve the actual contents of the |
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613 |
``date_updated`` property of the ``blog_entry`` object. This can be |
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614 |
accomplished by using the ``Variable()`` class in ``django.template``. |
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615 |
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616 |
To use the ``Variable`` class, simply instantiate it with the name of the |
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617 |
variable to be resolved, and then call ``variable.resolve(context)``. So, |
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618 |
for example:: |
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619 |
|
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620 |
class FormatTimeNode(template.Node): |
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621 |
def __init__(self, date_to_be_formatted, format_string): |
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622 |
self.date_to_be_formatted = template.Variable(date_to_be_formatted) |
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623 |
self.format_string = format_string |
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624 |
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625 |
def render(self, context): |
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626 |
try: |
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627 |
actual_date = self.date_to_be_formatted.resolve(context) |
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628 |
return actual_date.strftime(self.format_string) |
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629 |
except template.VariableDoesNotExist: |
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630 |
return '' |
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631 |
|
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632 |
Variable resolution will throw a ``VariableDoesNotExist`` exception if it cannot |
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633 |
resolve the string passed to it in the current context of the page. |
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634 |
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635 |
Shortcut for simple tags |
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636 |
~~~~~~~~~~~~~~~~~~~~~~~~ |
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|
637 |
|
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638 |
Many template tags take a number of arguments -- strings or a template variables |
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639 |
-- and return a string after doing some processing based solely on |
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640 |
the input argument and some external information. For example, the |
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641 |
``current_time`` tag we wrote above is of this variety: we give it a format |
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642 |
string, it returns the time as a string. |
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643 |
|
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644 |
To ease the creation of the types of tags, Django provides a helper function, |
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645 |
``simple_tag``. This function, which is a method of |
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646 |
``django.template.Library``, takes a function that accepts any number of |
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647 |
arguments, wraps it in a ``render`` function and the other necessary bits |
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648 |
mentioned above and registers it with the template system. |
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649 |
|
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650 |
Our earlier ``current_time`` function could thus be written like this:: |
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651 |
|
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652 |
def current_time(format_string): |
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653 |
return datetime.datetime.now().strftime(format_string) |
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654 |
|
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655 |
register.simple_tag(current_time) |
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656 |
|
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657 |
The decorator syntax also works:: |
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658 |
|
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659 |
@register.simple_tag |
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660 |
def current_time(format_string): |
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661 |
... |
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662 |
|
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663 |
A couple of things to note about the ``simple_tag`` helper function: |
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664 |
|
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665 |
* Checking for the required number of arguments, etc., has already been |
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666 |
done by the time our function is called, so we don't need to do that. |
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667 |
* The quotes around the argument (if any) have already been stripped away, |
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668 |
so we just receive a plain string. |
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669 |
* If the argument was a template variable, our function is passed the |
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670 |
current value of the variable, not the variable itself. |
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671 |
|
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672 |
When your template tag does not need access to the current context, writing a |
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673 |
function to work with the input values and using the ``simple_tag`` helper is |
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674 |
the easiest way to create a new tag. |
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675 |
|
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676 |
.. _howto-custom-template-tags-inclusion-tags: |
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677 |
|
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|
678 |
Inclusion tags |
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|
679 |
~~~~~~~~~~~~~~ |
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|
680 |
|
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681 |
Another common type of template tag is the type that displays some data by |
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682 |
rendering *another* template. For example, Django's admin interface uses custom |
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683 |
template tags to display the buttons along the bottom of the "add/change" form |
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684 |
pages. Those buttons always look the same, but the link targets change depending |
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685 |
on the object being edited -- so they're a perfect case for using a small |
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686 |
template that is filled with details from the current object. (In the admin's |
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687 |
case, this is the ``submit_row`` tag.) |
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688 |
|
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|
689 |
These sorts of tags are called "inclusion tags". |
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690 |
|
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691 |
Writing inclusion tags is probably best demonstrated by example. Let's write a |
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692 |
tag that outputs a list of choices for a given ``Poll`` object, such as was |
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693 |
created in the :ref:`tutorials <creating-models>`. We'll use the tag like this: |
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694 |
|
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695 |
.. code-block:: html+django |
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696 |
|
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697 |
{% show_results poll %} |
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698 |
|
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Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
699 |
...and the output will be something like this: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
700 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
701 |
.. code-block:: html |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
702 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
703 |
<ul> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
704 |
<li>First choice</li> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
705 |
<li>Second choice</li> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
706 |
<li>Third choice</li> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
707 |
</ul> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
708 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
709 |
First, define the function that takes the argument and produces a dictionary of |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
710 |
data for the result. The important point here is we only need to return a |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
711 |
dictionary, not anything more complex. This will be used as a template context |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
712 |
for the template fragment. Example:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
713 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
714 |
def show_results(poll): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
715 |
choices = poll.choice_set.all() |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
716 |
return {'choices': choices} |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
717 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
718 |
Next, create the template used to render the tag's output. This template is a |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
719 |
fixed feature of the tag: the tag writer specifies it, not the template |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
720 |
designer. Following our example, the template is very simple: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
721 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
722 |
.. code-block:: html+django |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
723 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
724 |
<ul> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
725 |
{% for choice in choices %} |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
726 |
<li> {{ choice }} </li> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
727 |
{% endfor %} |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
728 |
</ul> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
729 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
730 |
Now, create and register the inclusion tag by calling the ``inclusion_tag()`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
731 |
method on a ``Library`` object. Following our example, if the above template is |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
732 |
in a file called ``results.html`` in a directory that's searched by the template |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
733 |
loader, we'd register the tag like this:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
734 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
735 |
# Here, register is a django.template.Library instance, as before |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
736 |
register.inclusion_tag('results.html')(show_results) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
737 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
738 |
As always, decorator syntax works as well, so we could have written:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
739 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
740 |
@register.inclusion_tag('results.html') |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
741 |
def show_results(poll): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
742 |
... |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
743 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
744 |
...when first creating the function. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
745 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
746 |
Sometimes, your inclusion tags might require a large number of arguments, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
747 |
making it a pain for template authors to pass in all the arguments and remember |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
748 |
their order. To solve this, Django provides a ``takes_context`` option for |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
749 |
inclusion tags. If you specify ``takes_context`` in creating a template tag, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
750 |
the tag will have no required arguments, and the underlying Python function |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
751 |
will have one argument -- the template context as of when the tag was called. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
752 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
753 |
For example, say you're writing an inclusion tag that will always be used in a |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
754 |
context that contains ``home_link`` and ``home_title`` variables that point |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
755 |
back to the main page. Here's what the Python function would look like:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
756 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
757 |
# The first argument *must* be called "context" here. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
758 |
def jump_link(context): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
759 |
return { |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
760 |
'link': context['home_link'], |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
761 |
'title': context['home_title'], |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
762 |
} |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
763 |
# Register the custom tag as an inclusion tag with takes_context=True. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
764 |
register.inclusion_tag('link.html', takes_context=True)(jump_link) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
765 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
766 |
(Note that the first parameter to the function *must* be called ``context``.) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
767 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
768 |
In that ``register.inclusion_tag()`` line, we specified ``takes_context=True`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
769 |
and the name of the template. Here's what the template ``link.html`` might look |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
770 |
like: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
771 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
772 |
.. code-block:: html+django |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
773 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
774 |
Jump directly to <a href="{{ link }}">{{ title }}</a>. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
775 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
776 |
Then, any time you want to use that custom tag, load its library and call it |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
777 |
without any arguments, like so: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
778 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
779 |
.. code-block:: html+django |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
780 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
781 |
{% jump_link %} |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
782 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
783 |
Note that when you're using ``takes_context=True``, there's no need to pass |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
784 |
arguments to the template tag. It automatically gets access to the context. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
785 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
786 |
The ``takes_context`` parameter defaults to ``False``. When it's set to *True*, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
787 |
the tag is passed the context object, as in this example. That's the only |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
788 |
difference between this case and the previous ``inclusion_tag`` example. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
789 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
790 |
Setting a variable in the context |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
791 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
792 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
793 |
The above examples simply output a value. Generally, it's more flexible if your |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
794 |
template tags set template variables instead of outputting values. That way, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
795 |
template authors can reuse the values that your template tags create. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
796 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
797 |
To set a variable in the context, just use dictionary assignment on the context |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
798 |
object in the ``render()`` method. Here's an updated version of |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
799 |
``CurrentTimeNode`` that sets a template variable ``current_time`` instead of |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
800 |
outputting it:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
801 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
802 |
class CurrentTimeNode2(template.Node): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
803 |
def __init__(self, format_string): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
804 |
self.format_string = format_string |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
805 |
def render(self, context): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
806 |
context['current_time'] = datetime.datetime.now().strftime(self.format_string) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
807 |
return '' |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
808 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
809 |
Note that ``render()`` returns the empty string. ``render()`` should always |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
810 |
return string output. If all the template tag does is set a variable, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
811 |
``render()`` should return the empty string. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
812 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
813 |
Here's how you'd use this new version of the tag: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
814 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
815 |
.. code-block:: html+django |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
816 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
817 |
{% current_time "%Y-%M-%d %I:%M %p" %}<p>The time is {{ current_time }}.</p> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
818 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
819 |
.. admonition:: Variable scope in context |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
820 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
821 |
Any variable set in the context will only be available in the same ``block`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
822 |
of the template in which it was assigned. This behaviour is intentional; |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
823 |
it provides a scope for variables so that they don't conflict with |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
824 |
context in other blocks. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
825 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
826 |
But, there's a problem with ``CurrentTimeNode2``: The variable name |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
827 |
``current_time`` is hard-coded. This means you'll need to make sure your |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
828 |
template doesn't use ``{{ current_time }}`` anywhere else, because the |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
829 |
``{% current_time %}`` will blindly overwrite that variable's value. A cleaner |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
830 |
solution is to make the template tag specify the name of the output variable, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
831 |
like so: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
832 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
833 |
.. code-block:: html+django |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
834 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
835 |
{% current_time "%Y-%M-%d %I:%M %p" as my_current_time %} |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
836 |
<p>The current time is {{ my_current_time }}.</p> |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
837 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
838 |
To do that, you'll need to refactor both the compilation function and ``Node`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
839 |
class, like so:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
840 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
841 |
class CurrentTimeNode3(template.Node): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
842 |
def __init__(self, format_string, var_name): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
843 |
self.format_string = format_string |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
844 |
self.var_name = var_name |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
845 |
def render(self, context): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
846 |
context[self.var_name] = datetime.datetime.now().strftime(self.format_string) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
847 |
return '' |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
848 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
849 |
import re |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
850 |
def do_current_time(parser, token): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
851 |
# This version uses a regular expression to parse tag contents. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
852 |
try: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
853 |
# Splitting by None == splitting by spaces. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
854 |
tag_name, arg = token.contents.split(None, 1) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
855 |
except ValueError: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
856 |
raise template.TemplateSyntaxError, "%r tag requires arguments" % token.contents.split()[0] |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
857 |
m = re.search(r'(.*?) as (\w+)', arg) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
858 |
if not m: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
859 |
raise template.TemplateSyntaxError, "%r tag had invalid arguments" % tag_name |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
860 |
format_string, var_name = m.groups() |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
861 |
if not (format_string[0] == format_string[-1] and format_string[0] in ('"', "'")): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
862 |
raise template.TemplateSyntaxError, "%r tag's argument should be in quotes" % tag_name |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
863 |
return CurrentTimeNode3(format_string[1:-1], var_name) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
864 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
865 |
The difference here is that ``do_current_time()`` grabs the format string and |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
866 |
the variable name, passing both to ``CurrentTimeNode3``. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
867 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
868 |
Parsing until another block tag |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
869 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
870 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
871 |
Template tags can work in tandem. For instance, the standard ``{% comment %}`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
872 |
tag hides everything until ``{% endcomment %}``. To create a template tag such |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
873 |
as this, use ``parser.parse()`` in your compilation function. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
874 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
875 |
Here's how the standard ``{% comment %}`` tag is implemented:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
876 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
877 |
def do_comment(parser, token): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
878 |
nodelist = parser.parse(('endcomment',)) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
879 |
parser.delete_first_token() |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
880 |
return CommentNode() |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
881 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
882 |
class CommentNode(template.Node): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
883 |
def render(self, context): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
884 |
return '' |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
885 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
886 |
``parser.parse()`` takes a tuple of names of block tags ''to parse until''. It |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
887 |
returns an instance of ``django.template.NodeList``, which is a list of |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
888 |
all ``Node`` objects that the parser encountered ''before'' it encountered |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
889 |
any of the tags named in the tuple. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
890 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
891 |
In ``"nodelist = parser.parse(('endcomment',))"`` in the above example, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
892 |
``nodelist`` is a list of all nodes between the ``{% comment %}`` and |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
893 |
``{% endcomment %}``, not counting ``{% comment %}`` and ``{% endcomment %}`` |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
894 |
themselves. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
895 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
896 |
After ``parser.parse()`` is called, the parser hasn't yet "consumed" the |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
897 |
``{% endcomment %}`` tag, so the code needs to explicitly call |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
898 |
``parser.delete_first_token()``. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
899 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
900 |
``CommentNode.render()`` simply returns an empty string. Anything between |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
901 |
``{% comment %}`` and ``{% endcomment %}`` is ignored. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
902 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
903 |
Parsing until another block tag, and saving contents |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
904 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
905 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
906 |
In the previous example, ``do_comment()`` discarded everything between |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
907 |
``{% comment %}`` and ``{% endcomment %}``. Instead of doing that, it's |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
908 |
possible to do something with the code between block tags. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
909 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
910 |
For example, here's a custom template tag, ``{% upper %}``, that capitalizes |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
911 |
everything between itself and ``{% endupper %}``. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
912 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
913 |
Usage: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
914 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
915 |
.. code-block:: html+django |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
916 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
917 |
{% upper %}This will appear in uppercase, {{ your_name }}.{% endupper %} |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
918 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
919 |
As in the previous example, we'll use ``parser.parse()``. But this time, we |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
920 |
pass the resulting ``nodelist`` to the ``Node``:: |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
921 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
922 |
def do_upper(parser, token): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
923 |
nodelist = parser.parse(('endupper',)) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
924 |
parser.delete_first_token() |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
925 |
return UpperNode(nodelist) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
926 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
927 |
class UpperNode(template.Node): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
928 |
def __init__(self, nodelist): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
929 |
self.nodelist = nodelist |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
930 |
def render(self, context): |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
931 |
output = self.nodelist.render(context) |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
932 |
return output.upper() |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
933 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
934 |
The only new concept here is the ``self.nodelist.render(context)`` in |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
935 |
``UpperNode.render()``. |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
936 |
|
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
937 |
For more examples of complex rendering, see the source code for ``{% if %}``, |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
938 |
``{% for %}``, ``{% ifequal %}`` and ``{% ifchanged %}``. They live in |
c6bca38c1cbf
Added buildout stuff and made changes accordingly
Nishanth Amuluru <nishanth@fossee.in>
parents:
diff
changeset
|
939 |
``django/template/defaulttags.py``. |