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-:261778de26ff
+:620f9b141567
+====================
+The newforms library
+====================
+``django.newforms`` is Django's fantastic new form-handling library. It's a
+replacement for ``django.forms``, the old form/manipulator/validation
+framework. This document explains how to use this new library.
+Migration plan
+==============
+``django.newforms`` currently is only available in Django beginning
+with the 0.96 release.  the Django development version -- i.e., it's
+not available in the Django 0.95 release. For the next Django release,
+our plan is to do the following:
+* As of revision [4208], we've copied the current ``django.forms`` to
+``django.oldforms``. This allows you to upgrade your code *now* rather
+than waiting for the backwards-incompatible change and rushing to fix
+your code after the fact. Just change your import statements like this::
+from django import forms             # old
+from django import oldforms as forms # new
+* At an undecided future date, we will move the current ``django.newforms``
+to ``django.forms``. This will be a backwards-incompatible change, and
+anybody who is still using the old version of ``django.forms`` at that
+time will need to change their import statements, as described in the
+previous bullet.
+* We will remove ``django.oldforms`` in the release *after* the next Django
+release -- the release that comes after the release in which we're
+creating the new ``django.forms``.
+With this in mind, we recommend you use the following import statement when
+using ``django.newforms``::
+from django import newforms as forms
+This way, your code can refer to the ``forms`` module, and when
+``django.newforms`` is renamed to ``django.forms``, you'll only have to change
+your ``import`` statements.
+If you prefer "``import *``" syntax, you can do the following::
+from django.newforms import *
+This will import all fields, widgets, form classes and other various utilities
+into your local namespace. Some people find this convenient; others find it
+too messy. The choice is yours.
+Overview
+========
+As with the ``django.forms`` ("manipulators") system before it,
+``django.newforms`` is intended to handle HTML form display, data processing
+(validation) and redisplay. It's what you use if you want to perform
+server-side validation for an HTML form.
+For example, if your Web site has a contact form that visitors can use to
+send you e-mail, you'd use this library to implement the display of the HTML
+form fields, along with the form validation. Any time you need to use an HTML
+``<form>``, you can use this library.
+The library deals with these concepts:
+* **Widget** -- A class that corresponds to an HTML form widget, e.g.
+``<input type="text">`` or ``<textarea>``. This handles rendering of the
+widget as HTML.
+* **Field** -- A class that is responsible for doing validation, e.g.
+an ``EmailField`` that makes sure its data is a valid e-mail address.
+* **Form** -- A collection of fields that knows how to validate itself and
+display itself as HTML.
+The library is decoupled from the other Django components, such as the database
+layer, views and templates. It relies only on Django settings, a couple of
+``django.utils`` helper functions and Django's internationalization hooks (but
+you're not required to be using internationalization features to use this
+library).
+Form objects
+============
+The primary way of using the ``newforms`` library is to create a form object.
+Do this by subclassing ``django.newforms.Form`` and specifying the form's
+fields, in a declarative style that you'll be familiar with if you've used
+Django database models. In this section, we'll iteratively develop a form
+object that you might use to implement "contact me" functionality on your
+personal Web site.
+Start with this basic ``Form`` subclass, which we'll call ``ContactForm``::
+from django import newforms as forms
+class ContactForm(forms.Form):
+subject = forms.CharField(max_length=100)
+message = forms.CharField()
+sender = forms.EmailField()
+cc_myself = forms.BooleanField()
+A form is composed of ``Field`` objects. In this case, our form has four
+fields: ``subject``, ``message``, ``sender`` and ``cc_myself``. We'll explain
+the different types of fields -- e.g., ``CharField`` and ``EmailField`` --
+shortly.
+Creating ``Form`` instances
+---------------------------
+A ``Form`` instance is either **bound** or **unbound** to a set of data.
+* If it's **bound** to a set of data, it's capable of validating that data
+and rendering the form as HTML with the data displayed in the HTML.
+* If it's **unbound**, it cannot do validation (because there's no data to
+validate!), but it can still render the blank form as HTML.
+To create an unbound ``Form`` instance, simply instantiate the class::
+>>> f = ContactForm()
+To bind data to a form, pass the data as a dictionary as the first parameter to
+your ``Form`` class constructor::
+>>> data = {'subject': 'hello',
+...         'message': 'Hi there',
+...         'sender': 'foo@example.com',
+...         'cc_myself': True}
+>>> f = ContactForm(data)
+In this dictionary, the keys are the field names, which correspond to the
+attributes in your ``Form`` class. The values are the data you're trying
+to validate. These will usually be strings, but there's no requirement that
+they be strings; the type of data you pass depends on the ``Field``, as we'll
+see in a moment.
+If you need to distinguish between bound and unbound form instances at runtime,
+check the value of the form's ``is_bound`` attribute::
+>>> f = ContactForm()
+>>> f.is_bound
+False
+>>> f = ContactForm({'subject': 'hello'})
+>>> f.is_bound
+True
+Note that passing an empty dictionary creates a *bound* form with empty data::
+>>> f = ContactForm({})
+>>> f.is_bound
+True
+If you have a bound ``Form`` instance and want to change the data somehow, or
+if you want to bind an unbound ``Form`` instance to some data, create another
+``Form`` instance. There is no way to change data in a ``Form`` instance. Once
+a ``Form`` instance has been created, you should consider its data immutable,
+whether it has data or not.
+Using forms to validate data
+----------------------------
+The primary task of a ``Form`` object is to validate data. With a bound
+``Form`` instance, call the ``is_valid()`` method to run validation and return
+a boolean designating whether the data was valid::
+>>> data = {'subject': 'hello',
+...         'message': 'Hi there',
+...         'sender': 'foo@example.com',
+...         'cc_myself': True}
+>>> f = ContactForm(data)
+>>> f.is_valid()
+True
+Let's try with some invalid data. In this case, ``subject`` is blank (an error,
+because all fields are required by default) and ``sender`` is not a valid
+e-mail address::
+>>> data = {'subject': '',
+...         'message': 'Hi there',
+...         'sender': 'invalid e-mail address',
+...         'cc_myself': True}
+>>> f = ContactForm(data)
+>>> f.is_valid()
+False
+Access the ``Form`` attribute ``errors`` to get a dictionary of error messages::
+>>> f.errors
+{'sender': [u'Enter a valid e-mail address.'], 'subject': [u'This field is required.']}
+In this dictionary, the keys are the field names, and the values are lists of
+Unicode strings representing the error messages. The error messages are stored
+in lists because a field can have multiple error messages.
+You can access ``errors`` without having to call ``is_valid()`` first. The
+form's data will be validated the first time either you call ``is_valid()`` or
+access ``errors``.
+Behavior of unbound forms
+~~~~~~~~~~~~~~~~~~~~~~~~~
+It's meaningless to validate a form with no data, but, for the record, here's
+what happens with unbound forms::
+>>> f = ContactForm()
+>>> f.is_valid()
+False
+>>> f.errors
+{}
+Accessing "clean" data
+----------------------
+Each ``Field`` in a ``Form`` class is responsible not only for validating data,
+but also for "cleaning" it -- normalizing it to a consistent format. This is a
+nice feature, because it allows data for a particular field to be input in
+a variety of ways, always resulting in consistent output.
+For example, ``DateField`` normalizes input into a Python ``datetime.date``
+object. Regardless of whether you pass it a string in the format
+``'1994-07-15'``, a ``datetime.date`` object or a number of other formats,
+``DateField`` will always normalize it to a ``datetime.date`` object as long as
+it's valid.
+Once you've created a ``Form`` instance with a set of data and validated it,
+you can access the clean data via the ``clean_data`` attribute of the ``Form``
+object::
+>>> data = {'subject': 'hello',
+...         'message': 'Hi there',
+...         'sender': 'foo@example.com',
+...         'cc_myself': True}
+>>> f = ContactForm(data)
+>>> f.is_valid()
+True
+>>> f.clean_data
+{'cc_myself': True, 'message': u'Hi there', 'sender': u'foo@example.com', 'subject': u'hello'}
+Note that any text-based field -- such as ``CharField`` or ``EmailField`` --
+always cleans the input into a Unicode string. We'll cover the encoding
+implications later in this document.
+If your data does *not* validate, your ``Form`` instance will not have a
+``clean_data`` attribute::
+>>> data = {'subject': '',
+...         'message': 'Hi there',
+...         'sender': 'invalid e-mail address',
+...         'cc_myself': True}
+>>> f = ContactForm(data)
+>>> f.is_valid()
+False
+>>> f.clean_data
+Traceback (most recent call last):
+...
+AttributeError: 'ContactForm' object has no attribute 'clean_data'
+``clean_data`` will always *only* contain a key for fields defined in the
+``Form``, even if you pass extra data when you define the ``Form``. In this
+example, we pass a bunch of extra fields to the ``ContactForm`` constructor,
+but ``clean_data`` contains only the form's fields::
+>>> data = {'subject': 'hello',
+...         'message': 'Hi there',
+...         'sender': 'foo@example.com',
+...         'cc_myself': True,
+...         'extra_field_1': 'foo',
+...         'extra_field_2': 'bar',
+...         'extra_field_3': 'baz'}
+>>> f = ContactForm(data)
+>>> f.is_valid()
+True
+>>> f.clean_data # Doesn't contain extra_field_1, etc.
+{'cc_myself': True, 'message': u'Hi there', 'sender': u'foo@example.com', 'subject': u'hello'}
+Behavior of unbound forms
+~~~~~~~~~~~~~~~~~~~~~~~~~
+It's meaningless to request "clean" data in a form with no data, but, for the
+record, here's what happens with unbound forms::
+>>> f = ContactForm()
+>>> f.clean_data
+Traceback (most recent call last):
+...
+AttributeError: 'ContactForm' object has no attribute 'clean_data'
+Outputting forms as HTML
+------------------------
+The second task of a ``Form`` object is to render itself as HTML. To do so,
+simply ``print`` it::
+>>> f = ContactForm()
+>>> print f
+<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" /></td></tr>
+<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" /></td></tr>
+<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" /></td></tr>
+<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself" /></td></tr>
+If the form is bound to data, the HTML output will include that data
+appropriately. For example, if a field is represented by an
+``<input type="text">``, the data will be in the ``value`` attribute. If a
+field is represented by an ``<input type="checkbox">``, then that HTML will
+include ``checked="checked"`` if appropriate::
+>>> data = {'subject': 'hello',
+...         'message': 'Hi there',
+...         'sender': 'foo@example.com',
+...         'cc_myself': True}
+>>> f = ContactForm(data)
+>>> print f
+<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" value="hello" /></td></tr>
+<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" value="Hi there" /></td></tr>
+<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" value="foo@example.com" /></td></tr>
+<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself" checked="checked" /></td></tr>
+This default output is a two-column HTML table, with a ``<tr>`` for each field.
+Notice the following:
+* For flexibility, the output does *not* include the ``<table>`` and
+``</table>`` tags, nor does it include the ``<form>`` and ``</form>``
+tags or an ``<input type="submit">`` tag. It's your job to do that.
+* Each field type has a default HTML representation. ``CharField`` and
+``EmailField`` are represented by an ``<input type="text">``.
+``BooleanField`` is represented by an ``<input type="checkbox">``. Note
+these are merely sensible defaults; you can specify which HTML to use for
+a given field by using widgets, which we'll explain shortly.
+* The HTML ``name`` for each tag is taken directly from its attribute name
+in the ``ContactForm`` class.
+* The text label for each field -- e.g. ``'Subject:'``, ``'Message:'`` and
+``'Cc myself:'`` is generated from the field name by converting all
+underscores to spaces and upper-casing the first letter. Again, note
+these are merely sensible defaults; you can also specify labels manually.
+* Each text label is surrounded in an HTML ``<label>`` tag, which points
+to the appropriate form field via its ``id``. Its ``id``, in turn, is
+generated by prepending ``'id_'`` to the field name. The ``id``
+attributes and ``<label>`` tags are included in the output by default, to
+follow best practices, but you can change that behavior.
+Although ``<table>`` output is the default output style when you ``print`` a
+form, other output styles are available. Each style is available as a method on
+a form object, and each rendering method returns a Unicode object.
+``as_p()``
+~~~~~~~~~~
+``Form.as_p()`` renders the form as a series of ``<p>`` tags, with each ``<p>``
+containing one field::
+>>> f = ContactForm()
+>>> f.as_p()
+u'<p><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" /></p>\n<p><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></p>\n<p><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></p>\n<p><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself" /></p>'
+>>> print f.as_p()
+<p><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" /></p>
+<p><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></p>
+<p><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></p>
+<p><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself" /></p>
+``as_ul()``
+~~~~~~~~~~~
+``Form.as_ul()`` renders the form as a series of ``<li>`` tags, with each
+``<li>`` containing one field. It does *not* include the ``<ul>`` or ``</ul>``,
+so that you can specify any HTML attributes on the ``<ul>`` for flexibility::
+>>> f = ContactForm()
+>>> f.as_ul()
+u'<li><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" /></li>\n<li><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></li>\n<li><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></li>\n<li><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself" /></li>'
+>>> print f.as_ul()
+<li><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" /></li>
+<li><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></li>
+<li><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></li>
+<li><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself" /></li>
+``as_table()``
+~~~~~~~~~~~~~~
+Finally, ``Form.as_table()`` outputs the form as an HTML ``<table>``. This is
+exactly the same as ``print``. In fact, when you ``print`` a form object, it
+calls its ``as_table()`` method behind the scenes::
+>>> f = ContactForm()
+>>> f.as_table()
+u'<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" /></td></tr>\n<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" /></td></tr>\n<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" /></td></tr>\n<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself" /></td></tr>'
+>>> print f.as_table()
+<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" /></td></tr>
+<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" /></td></tr>
+<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" /></td></tr>
+<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself" /></td></tr>
+Configuring HTML ``<label>`` tags
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+An HTML ``<label>`` tag designates which label text is associated with which
+form element. This small enhancement makes forms more usable and more accessible
+to assistive devices. It's always a good idea to use ``<label>`` tags.
+By default, the form rendering methods include HTML ``id`` attributes on the
+form elements and corresponding ``<label>`` tags around the labels. The ``id``
+attribute values are generated by prepending ``id_`` to the form field names.
+This behavior is configurable, though, if you want to change the ``id``
+convention or remove HTML ``id`` attributes and ``<label>`` tags entirely.
+Use the ``auto_id`` argument to the ``Form`` constructor to control the label
+and ``id`` behavior. This argument must be ``True``, ``False`` or a string.
+If ``auto_id`` is ``False``, then the form output will not include ``<label>``
+tags nor ``id`` attributes::
+>>> f = ContactForm(auto_id=False)
+>>> print f.as_table()
+<tr><th>Subject:</th><td><input type="text" name="subject" maxlength="100" /></td></tr>
+<tr><th>Message:</th><td><input type="text" name="message" /></td></tr>
+<tr><th>Sender:</th><td><input type="text" name="sender" /></td></tr>
+<tr><th>Cc myself:</th><td><input type="checkbox" name="cc_myself" /></td></tr>
+>>> print f.as_ul()
+<li>Subject: <input type="text" name="subject" maxlength="100" /></li>
+<li>Message: <input type="text" name="message" /></li>
+<li>Sender: <input type="text" name="sender" /></li>
+<li>Cc myself: <input type="checkbox" name="cc_myself" /></li>
+>>> print f.as_p()
+<p>Subject: <input type="text" name="subject" maxlength="100" /></p>
+<p>Message: <input type="text" name="message" /></p>
+<p>Sender: <input type="text" name="sender" /></p>
+<p>Cc myself: <input type="checkbox" name="cc_myself" /></p>
+If ``auto_id`` is set to ``True``, then the form output *will* include
+``<label>`` tags and will simply use the field name as its ``id`` for each form
+field::
+>>> f = ContactForm(auto_id=True)
+>>> print f.as_table()
+<tr><th><label for="subject">Subject:</label></th><td><input id="subject" type="text" name="subject" maxlength="100" /></td></tr>
+<tr><th><label for="message">Message:</label></th><td><input type="text" name="message" id="message" /></td></tr>
+<tr><th><label for="sender">Sender:</label></th><td><input type="text" name="sender" id="sender" /></td></tr>
+<tr><th><label for="cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="cc_myself" /></td></tr>
+>>> print f.as_ul()
+<li><label for="subject">Subject:</label> <input id="subject" type="text" name="subject" maxlength="100" /></li>
+<li><label for="message">Message:</label> <input type="text" name="message" id="message" /></li>
+<li><label for="sender">Sender:</label> <input type="text" name="sender" id="sender" /></li>
+<li><label for="cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="cc_myself" /></li>
+>>> print f.as_p()
+<p><label for="subject">Subject:</label> <input id="subject" type="text" name="subject" maxlength="100" /></p>
+<p><label for="message">Message:</label> <input type="text" name="message" id="message" /></p>
+<p><label for="sender">Sender:</label> <input type="text" name="sender" id="sender" /></p>
+<p><label for="cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="cc_myself" /></p>
+If ``auto_id`` is set to a string containing the format character ``'%s'``,
+then the form output will include ``<label>`` tags, and will generate ``id``
+attributes based on the format string. For example, for a format string
+``'field_%s'``, a field named ``subject`` will get the ``id``
+``'field_subject'``. Continuing our example::
+>>> f = ContactForm(auto_id='id_for_%s')
+>>> print f.as_table()
+<tr><th><label for="id_for_subject">Subject:</label></th><td><input id="id_for_subject" type="text" name="subject" maxlength="100" /></td></tr>
+<tr><th><label for="id_for_message">Message:</label></th><td><input type="text" name="message" id="id_for_message" /></td></tr>
+<tr><th><label for="id_for_sender">Sender:</label></th><td><input type="text" name="sender" id="id_for_sender" /></td></tr>
+<tr><th><label for="id_for_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></td></tr>
+>>> print f.as_ul()
+<li><label for="id_for_subject">Subject:</label> <input id="id_for_subject" type="text" name="subject" maxlength="100" /></li>
+<li><label for="id_for_message">Message:</label> <input type="text" name="message" id="id_for_message" /></li>
+<li><label for="id_for_sender">Sender:</label> <input type="text" name="sender" id="id_for_sender" /></li>
+<li><label for="id_for_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></li>
+>>> print f.as_p()
+<p><label for="id_for_subject">Subject:</label> <input id="id_for_subject" type="text" name="subject" maxlength="100" /></p>
+<p><label for="id_for_message">Message:</label> <input type="text" name="message" id="id_for_message" /></p>
+<p><label for="id_for_sender">Sender:</label> <input type="text" name="sender" id="id_for_sender" /></p>
+<p><label for="id_for_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></p>
+If ``auto_id`` is set to any other true value -- such as a string that doesn't
+include ``%s`` -- then the library will act as if ``auto_id`` is ``True``.
+By default, ``auto_id`` is set to the string ``'id_%s'``.
+Notes on field ordering
+~~~~~~~~~~~~~~~~~~~~~~~
+In the ``as_p()``, ``as_ul()`` and ``as_table()`` shortcuts, the fields are
+displayed in the order in which you define them in your form class. For
+example, in the ``ContactForm`` example, the fields are defined in the order
+``subject``, ``message``, ``sender``, ``cc_myself``. To reorder the HTML
+output, just change the order in which those fields are listed in the class.
+How errors are displayed
+~~~~~~~~~~~~~~~~~~~~~~~~
+If you render a bound ``Form`` object, the act of rendering will automatically
+run the form's validation if it hasn't already happened, and the HTML output
+will include the validation errors as a ``<ul>`` near the field. The particular
+positioning of the error messages depends on the output method you're using::
+>>> data = {'subject': '',
+...         'message': 'Hi there',
+...         'sender': 'invalid e-mail address',
+...         'cc_myself': True}
+>>> f = ContactForm(data, auto_id=False)
+>>> print f.as_table()
+<tr><th>Subject:</th><td><ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="subject" maxlength="100" /></td></tr>
+<tr><th>Message:</th><td><input type="text" name="message" value="Hi there" /></td></tr>
+<tr><th>Sender:</th><td><ul class="errorlist"><li>Enter a valid e-mail address.</li></ul><input type="text" name="sender" value="invalid e-mail address" /></td></tr>
+<tr><th>Cc myself:</th><td><input checked="checked" type="checkbox" name="cc_myself" /></td></tr>
+>>> print f.as_ul()
+<li><ul class="errorlist"><li>This field is required.</li></ul>Subject: <input type="text" name="subject" maxlength="100" /></li>
+<li>Message: <input type="text" name="message" value="Hi there" /></li>
+<li><ul class="errorlist"><li>Enter a valid e-mail address.</li></ul>Sender: <input type="text" name="sender" value="invalid e-mail address" /></li>
+<li>Cc myself: <input checked="checked" type="checkbox" name="cc_myself" /></li>
+>>> print f.as_p()
+<p><ul class="errorlist"><li>This field is required.</li></ul></p>
+<p>Subject: <input type="text" name="subject" maxlength="100" /></p>
+<p>Message: <input type="text" name="message" value="Hi there" /></p>
+<p><ul class="errorlist"><li>Enter a valid e-mail address.</li></ul></p>
+<p>Sender: <input type="text" name="sender" value="invalid e-mail address" /></p>
+<p>Cc myself: <input checked="checked" type="checkbox" name="cc_myself" /></p>
+More granular output
+~~~~~~~~~~~~~~~~~~~~
+The ``as_p()``, ``as_ul()`` and ``as_table()`` methods are simply shortcuts for
+lazy developers -- they're not the only way a form object can be displayed.
+To display the HTML for a single field in your form, use dictionary lookup
+syntax using the field's name as the key, and print the resulting object::
+>>> f = ContactForm()
+>>> print f['subject']
+<input id="id_subject" type="text" name="subject" maxlength="100" />
+>>> print f['message']
+<input type="text" name="message" id="id_message" />
+>>> print f['sender']
+<input type="text" name="sender" id="id_sender" />
+>>> print f['cc_myself']
+<input type="checkbox" name="cc_myself" id="id_cc_myself" />
+Call ``str()`` or ``unicode()`` on the field to get its rendered HTML as a
+string or Unicode object, respectively::
+>>> str(f['subject'])
+'<input id="id_subject" type="text" name="subject" maxlength="100" />'
+>>> unicode(f['subject'])
+u'<input id="id_subject" type="text" name="subject" maxlength="100" />'
+The field-specific output honors the form object's ``auto_id`` setting::
+>>> f = ContactForm(auto_id=False)
+>>> print f['message']
+<input type="text" name="message" />
+>>> f = ContactForm(auto_id='id_%s')
+>>> print f['message']
+<input type="text" name="message" id="id_message" />
+For a field's list of errors, access the field's ``errors`` attribute. This
+is a list-like object that is displayed as an HTML ``<ul>`` when printed::
+>>> data = {'subject': 'hi', 'message': '', 'sender': '', 'cc_myself': ''}
+>>> f = ContactForm(data, auto_id=False)
+>>> print f['message']
+<input type="text" name="message" />
+>>> f['message'].errors
+[u'This field is required.']
+>>> print f['message'].errors
+<ul class="errorlist"><li>This field is required.</li></ul>
+>>> f['subject'].errors
+[]
+>>> print f['subject'].errors
+>>> str(f['subject'].errors)
+''
+Subclassing forms
+-----------------
+If you subclass a custom ``Form`` class, the resulting ``Form`` class will
+include all fields of the parent class(es), followed by the fields you define
+in the subclass.
+In this example, ``ContactFormWithPriority`` contains all the fields from
+``ContactForm``, plus an additional field, ``priority``. The ``ContactForm``
+fields are ordered first::
+>>> class ContactFormWithPriority(ContactForm):
+...     priority = forms.CharField()
+>>> f = ContactFormWithPriority(auto_id=False)
+>>> print f.as_ul()
+<li>Subject: <input type="text" name="subject" maxlength="100" /></li>
+<li>Message: <input type="text" name="message" /></li>
+<li>Sender: <input type="text" name="sender" /></li>
+<li>Cc myself: <input type="checkbox" name="cc_myself" /></li>
+<li>Priority: <input type="text" name="priority" /></li>
+It's possible to subclass multiple forms, treating forms as "mix-ins." In this
+example, ``BeatleForm`` subclasses both ``PersonForm`` and ``InstrumentForm``
+(in that order), and its field list includes the fields from the parent
+classes::
+>>> class PersonForm(Form):
+...     first_name = CharField()
+...     last_name = CharField()
+>>> class InstrumentForm(Form):
+...     instrument = CharField()
+>>> class BeatleForm(PersonForm, InstrumentForm):
+...     haircut_type = CharField()
+>>> b = BeatleForm(auto_id=False)
+>>> print b.as_ul()
+<li>First name: <input type="text" name="first_name" /></li>
+<li>Last name: <input type="text" name="last_name" /></li>
+<li>Instrument: <input type="text" name="instrument" /></li>
+<li>Haircut type: <input type="text" name="haircut_type" /></li>
+Fields
+======
+When you create a ``Form`` class, the most important part is defining the
+fields of the form. Each field has custom validation logic, along with a few
+other hooks.
+Although the primary way you'll use ``Field`` classes is in ``Form`` classes,
+you can also instantiate them and use them directly to get a better idea of
+how they work. Each ``Field`` instance has a ``clean()`` method, which takes
+a single argument and either raises a ``django.newforms.ValidationError``
+exception or returns the clean value::
+>>> f = forms.EmailField()
+>>> f.clean('foo@example.com')
+u'foo@example.com'
+>>> f.clean(u'foo@example.com')
+u'foo@example.com'
+>>> f.clean('invalid e-mail address')
+Traceback (most recent call last):
+...
+ValidationError: [u'Enter a valid e-mail address.']
+If you've used Django's old forms/validation framework, take care in noticing
+this ``ValidationError`` is different than the previous ``ValidationError``.
+This one lives at ``django.newforms.ValidationError`` rather than
+``django.core.validators.ValidationError``.
+Core field arguments
+--------------------
+Each ``Field`` class constructor takes at least these arguments. Some
+``Field`` classes take additional, field-specific arguments, but the following
+should *always* be available:
+``required``
+~~~~~~~~~~~~
+By default, each ``Field`` class assumes the value is required, so if you pass
+an empty value -- either ``None`` or the empty string (``""``) -- then
+``clean()`` will raise a ``ValidationError`` exception::
+>>> f = forms.CharField()
+>>> f.clean('foo')
+u'foo'
+>>> f.clean('')
+Traceback (most recent call last):
+...
+ValidationError: [u'This field is required.']
+>>> f.clean(None)
+Traceback (most recent call last):
+...
+ValidationError: [u'This field is required.']
+>>> f.clean(' ')
+u' '
+>>> f.clean(0)
+u'0'
+>>> f.clean(True)
+u'True'
+>>> f.clean(False)
+u'False'
+To specify that a field is *not* required, pass ``required=False`` to the
+``Field`` constructor::
+>>> f = forms.CharField(required=False)
+>>> f.clean('foo')
+u'foo'
+>>> f.clean('')
+u''
+>>> f.clean(None)
+u''
+>>> f.clean(0)
+u'0'
+>>> f.clean(True)
+u'True'
+>>> f.clean(False)
+u'False'
+If a ``Field`` has ``required=False`` and you pass ``clean()`` an empty value,
+then ``clean()`` will return a *normalized* empty value rather than raising
+``ValidationError``. For ``CharField``, this will be a Unicode empty string.
+For other ``Field`` classes, it might be ``None``. (This varies from field to
+field.)
+``label``
+~~~~~~~~~
+The ``label`` argument lets you specify the "human-friendly" label for this
+field. This is used when the ``Field`` is displayed in a ``Form``.
+As explained in _`Outputting forms as HTML` above, the default label for a
+``Field`` is generated from the field name by converting all underscores to
+spaces and upper-casing the first letter. Specify ``label`` if that default
+behavior doesn't result in an adequate label.
+Here's a full example ``Form`` that implements ``label`` for two of its fields.
+We've specified ``auto_id=False`` to simplify the output::
+>>> class CommentForm(forms.Form):
+...     name = forms.CharField(label='Your name')
+...     url = forms.URLField(label='Your Web site', required=False)
+...     comment = forms.CharField()
+>>> f = CommentForm(auto_id=False)
+>>> print f
+<tr><th>Your name:</th><td><input type="text" name="name" /></td></tr>
+<tr><th>Your Web site:</th><td><input type="text" name="url" /></td></tr>
+<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
+``initial``
+~~~~~~~~~~~
+The ``initial`` argument lets you specify the initial value to use when
+rendering this ``Field`` in an unbound ``Form``.
+The use-case for this is when you want to display an "empty" form in which a
+field is initialized to a particular value. For example::
+>>> class CommentForm(forms.Form):
+...     name = forms.CharField(initial='Your name')
+...     url = forms.URLField(initial='http://')
+...     comment = forms.CharField()
+>>> f = CommentForm(auto_id=False)
+>>> print f
+<tr><th>Name:</th><td><input type="text" name="name" value="Your name" /></td></tr>
+<tr><th>Url:</th><td><input type="text" name="url" value="http://" /></td></tr>
+<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
+You may be thinking, why not just pass a dictionary of the initial values as
+data when displaying the form? Well, if you do that, you'll trigger validation,
+and the HTML output will include any validation errors::
+>>> class CommentForm(forms.Form):
+...     name = forms.CharField()
+...     url = forms.URLField()
+...     comment = forms.CharField()
+>>> default_data = {'name': 'Your name', 'url': 'http://'}
+>>> f = CommentForm(default_data, auto_id=False)
+>>> print f
+<tr><th>Name:</th><td><input type="text" name="name" value="Your name" /></td></tr>
+<tr><th>Url:</th><td><ul class="errorlist"><li>Enter a valid URL.</li></ul><input type="text" name="url" value="http://" /></td></tr>
+<tr><th>Comment:</th><td><ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="comment" /></td></tr>
+This is why ``initial`` values are only displayed for unbound forms. For bound
+forms, the HTML output will use the bound data.
+Also note that ``initial`` values are *not* used as "fallback" data in
+validation if a particular field's value is not given. ``initial`` values are
+*only* intended for initial form display::
+>>> class CommentForm(forms.Form):
+...     name = forms.CharField(initial='Your name')
+...     url = forms.URLField(initial='http://')
+...     comment = forms.CharField()
+>>> data = {'name': '', 'url': '', 'comment': 'Foo'}
+>>> f = CommentForm(data)
+>>> f.is_valid()
+False
+# The form does *not* fall back to using the initial values.
+>>> f.errors
+{'url': [u'This field is required.'], 'name': [u'This field is required.']}
+``widget``
+~~~~~~~~~~
+The ``widget`` argument lets you specify a ``Widget`` class to use when
+rendering this ``Field``. See _`Widgets` below for more information.
+``help_text``
+~~~~~~~~~~~~~
+The ``help_text`` argument lets you specify descriptive text for this
+``Field``. If you provide ``help_text``, it will be displayed next to the
+``Field`` when the ``Field`` is rendered in a ``Form``.
+Here's a full example ``Form`` that implements ``help_text`` for two of its
+fields. We've specified ``auto_id=False`` to simplify the output::
+>>> class HelpTextContactForm(forms.Form):
+...     subject = forms.CharField(max_length=100, help_text='100 characters max.')
+...     message = forms.CharField()
+...     sender = forms.EmailField(help_text='A valid e-mail address, please.')
+...     cc_myself = forms.BooleanField()
+>>> f = HelpTextContactForm(auto_id=False)
+>>> print f.as_table()
+<tr><th>Subject:</th><td><input type="text" name="subject" maxlength="100" /><br />100 characters max.</td></tr>
+<tr><th>Message:</th><td><input type="text" name="message" /></td></tr>
+<tr><th>Sender:</th><td><input type="text" name="sender" /><br />A valid e-mail address, please.</td></tr>
+<tr><th>Cc myself:</th><td><input type="checkbox" name="cc_myself" /></td></tr>
+>>> print f.as_ul()
+<li>Subject: <input type="text" name="subject" maxlength="100" /> 100 characters max.</li>
+<li>Message: <input type="text" name="message" /></li>
+<li>Sender: <input type="text" name="sender" /> A valid e-mail address, please.</li>
+<li>Cc myself: <input type="checkbox" name="cc_myself" /></li>
+>>> print f.as_p()
+<p>Subject: <input type="text" name="subject" maxlength="100" /> 100 characters max.</p>
+<p>Message: <input type="text" name="message" /></p>
+<p>Sender: <input type="text" name="sender" /> A valid e-mail address, please.</p>
+<p>Cc myself: <input type="checkbox" name="cc_myself" /></p>
+Dynamic initial values
+----------------------
+The ``initial`` argument to ``Field`` (explained above) lets you hard-code the
+initial value for a ``Field`` -- but what if you want to declare the initial
+value at runtime? For example, you might want to fill in a ``username`` field
+with the username of the current session.
+To accomplish this, use the ``initial`` argument to a ``Form``. This argument,
+if given, should be a dictionary mapping field names to initial values. Only
+include the fields for which you're specifying an initial value; it's not
+necessary to include every field in your form. For example::
+>>> class CommentForm(forms.Form):
+...     name = forms.CharField()
+...     url = forms.URLField()
+...     comment = forms.CharField()
+>>> f = CommentForm(initial={'name': 'your username'}, auto_id=False)
+>>> print f
+<tr><th>Name:</th><td><input type="text" name="name" value="your username" /></td></tr>
+<tr><th>Url:</th><td><input type="text" name="url" /></td></tr>
+<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
+>>> f = CommentForm(initial={'name': 'another username'}, auto_id=False)
+>>> print f
+<tr><th>Name:</th><td><input type="text" name="name" value="another username" /></td></tr>
+<tr><th>Url:</th><td><input type="text" name="url" /></td></tr>
+<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
+Just like the ``initial`` parameter to ``Field``, these values are only
+displayed for unbound forms, and they're not used as fallback values if a
+particular value isn't provided.
+Finally, note that if a ``Field`` defines ``initial`` *and* you include
+``initial`` when instantiating the ``Form``, then the latter ``initial`` will
+have precedence. In this example, ``initial`` is provided both at the field
+level and at the form instance level, and the latter gets precedence::
+>>> class CommentForm(forms.Form):
+...     name = forms.CharField(initial='class')
+...     url = forms.URLField()
+...     comment = forms.CharField()
+>>> f = CommentForm(initial={'name': 'instance'}, auto_id=False)
+>>> print f
+<tr><th>Name:</th><td><input type="text" name="name" value="instance" /></td></tr>
+<tr><th>Url:</th><td><input type="text" name="url" /></td></tr>
+<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
+More coming soon
+================
+That's all the documentation for now. For more, see the file
+http://code.djangoproject.com/browser/django/trunk/tests/regressiontests/forms/tests.py
+-- the unit tests for ``django.newforms``. This can give you a good idea of
+what's possible.
+If you're really itching to learn and use this library, please be patient.
+We're working hard on finishing both the code and documentation.
+Widgets
+=======