============

Unicode data

============

.. versionadded:: 1.0

Django natively supports Unicode data everywhere. Providing your database can

somehow store the data, you can safely pass around Unicode strings to

templates, models and the database.

This document tells you what you need to know if you're writing applications

that use data or templates that are encoded in something other than ASCII.

Creating the database

=====================

Make sure your database is configured to be able to store arbitrary string

data. Normally, this means giving it an encoding of UTF-8 or UTF-16. If you use

a more restrictive encoding -- for example, latin1 (iso8859-1) -- you won't be

able to store certain characters in the database, and information will be lost.

 * MySQL users, refer to the `MySQL manual`_ (section 9.1.3.2 for MySQL 5.1)

   for details on how to set or alter the database character set encoding.

 * PostgreSQL users, refer to the `PostgreSQL manual`_ (section 21.2.2 in

   PostgreSQL 8) for details on creating databases with the correct encoding.

 * SQLite users, there is nothing you need to do. SQLite always uses UTF-8

   for internal encoding.

.. _MySQL manual: http://dev.mysql.com/doc/refman/5.1/en/charset-database.html

.. _PostgreSQL manual: http://www.postgresql.org/docs/8.2/static/multibyte.html#AEN24104

All of Django's database backends automatically convert Unicode strings into

the appropriate encoding for talking to the database. They also automatically

convert strings retrieved from the database into Python Unicode strings. You

don't even need to tell Django what encoding your database uses: that is

handled transparently.

For more, see the section "The database API" below.

General string handling

=======================

Whenever you use strings with Django -- e.g., in database lookups, template

rendering or anywhere else -- you have two choices for encoding those strings.

You can use Unicode strings, or you can use normal strings (sometimes called

"bytestrings") that are encoded using UTF-8.

.. admonition:: Warning

    A bytestring does not carry any information with it about its encoding.

    For that reason, we have to make an assumption, and Django assumes that all

    bytestrings are in UTF-8.

    If you pass a string to Django that has been encoded in some other format,

    things will go wrong in interesting ways. Usually, Django will raise a

    ``UnicodeDecodeError`` at some point.

If your code only uses ASCII data, it's safe to use your normal strings,

passing them around at will, because ASCII is a subset of UTF-8.

Don't be fooled into thinking that if your :setting:`DEFAULT_CHARSET` setting is set

to something other than ``'utf-8'`` you can use that other encoding in your

bytestrings! :setting:`DEFAULT_CHARSET` only applies to the strings generated as

the result of template rendering (and e-mail). Django will always assume UTF-8

encoding for internal bytestrings. The reason for this is that the

:setting:`DEFAULT_CHARSET` setting is not actually under your control (if you are the

application developer). It's under the control of the person installing and

using your application -- and if that person chooses a different setting, your

code must still continue to work. Ergo, it cannot rely on that setting.

In most cases when Django is dealing with strings, it will convert them to

Unicode strings before doing anything else. So, as a general rule, if you pass

in a bytestring, be prepared to receive a Unicode string back in the result.

Translated strings

------------------

Aside from Unicode strings and bytestrings, there's a third type of string-like

object you may encounter when using Django. The framework's

internationalization features introduce the concept of a "lazy translation" --

a string that has been marked as translated but whose actual translation result

isn't determined until the object is used in a string. This feature is useful

in cases where the translation locale is unknown until the string is used, even

though the string might have originally been created when the code was first

imported.

Normally, you won't have to worry about lazy translations. Just be aware that

if you examine an object and it claims to be a

``django.utils.functional.__proxy__`` object, it is a lazy translation.

Calling ``unicode()`` with the lazy translation as the argument will generate a

Unicode string in the current locale.

For more details about lazy translation objects, refer to the

:doc:`internationalization </topics/i18n/index>` documentation.

Useful utility functions

------------------------

Because some string operations come up again and again, Django ships with a few

useful functions that should make working with Unicode and bytestring objects

a bit easier.

Conversion functions

~~~~~~~~~~~~~~~~~~~~

The ``django.utils.encoding`` module contains a few functions that are handy

for converting back and forth between Unicode and bytestrings.

    * ``smart_unicode(s, encoding='utf-8', strings_only=False, errors='strict')``

      converts its input to a Unicode string. The ``encoding`` parameter

      specifies the input encoding. (For example, Django uses this internally

      when processing form input data, which might not be UTF-8 encoded.) The

      ``strings_only`` parameter, if set to True, will result in Python

      numbers, booleans and ``None`` not being converted to a string (they keep

      their original types). The ``errors`` parameter takes any of the values

      that are accepted by Python's ``unicode()`` function for its error

      handling.

      If you pass ``smart_unicode()`` an object that has a ``__unicode__``

      method, it will use that method to do the conversion.

    * ``force_unicode(s, encoding='utf-8', strings_only=False,

      errors='strict')`` is identical to ``smart_unicode()`` in almost all

      cases. The difference is when the first argument is a :ref:`lazy

      translation <lazy-translations>` instance. While ``smart_unicode()``

      preserves lazy translations, ``force_unicode()`` forces those objects to a

      Unicode string (causing the translation to occur). Normally, you'll want

      to use ``smart_unicode()``. However, ``force_unicode()`` is useful in

      template tags and filters that absolutely *must* have a string to work

      with, not just something that can be converted to a string.

    * ``smart_str(s, encoding='utf-8', strings_only=False, errors='strict')``

      is essentially the opposite of ``smart_unicode()``. It forces the first

      argument to a bytestring. The ``strings_only`` parameter has the same

      behavior as for ``smart_unicode()`` and ``force_unicode()``. This is

      slightly different semantics from Python's builtin ``str()`` function,

      but the difference is needed in a few places within Django's internals.

Normally, you'll only need to use ``smart_unicode()``. Call it as early as

possible on any input data that might be either Unicode or a bytestring, and

from then on, you can treat the result as always being Unicode.

URI and IRI handling

~~~~~~~~~~~~~~~~~~~~

Web frameworks have to deal with URLs (which are a type of IRI_). One

requirement of URLs is that they are encoded using only ASCII characters.

However, in an international environment, you might need to construct a

URL from an IRI_ -- very loosely speaking, a URI that can contain Unicode

characters. Quoting and converting an IRI to URI can be a little tricky, so

Django provides some assistance.

    * The function ``django.utils.encoding.iri_to_uri()`` implements the

      conversion from IRI to URI as required by the specification (`RFC

      3987`_).

    * The functions ``django.utils.http.urlquote()`` and

      ``django.utils.http.urlquote_plus()`` are versions of Python's standard

      ``urllib.quote()`` and ``urllib.quote_plus()`` that work with non-ASCII

      characters. (The data is converted to UTF-8 prior to encoding.)

These two groups of functions have slightly different purposes, and it's

important to keep them straight. Normally, you would use ``urlquote()`` on the

individual portions of the IRI or URI path so that any reserved characters

such as '&' or '%' are correctly encoded. Then, you apply ``iri_to_uri()`` to

the full IRI and it converts any non-ASCII characters to the correct encoded

values.

.. note::

    Technically, it isn't correct to say that ``iri_to_uri()`` implements the

    full algorithm in the IRI specification. It doesn't (yet) perform the

    international domain name encoding portion of the algorithm.

The ``iri_to_uri()`` function will not change ASCII characters that are

otherwise permitted in a URL. So, for example, the character '%' is not

further encoded when passed to ``iri_to_uri()``. This means you can pass a

full URL to this function and it will not mess up the query string or anything

like that.

An example might clarify things here::

    >>> urlquote(u'Paris & Orléans')

    u'Paris%20%26%20Orl%C3%A9ans'

    >>> iri_to_uri(u'/favorites/François/%s' % urlquote(u'Paris & Orléans'))

    '/favorites/Fran%C3%A7ois/Paris%20%26%20Orl%C3%A9ans'

If you look carefully, you can see that the portion that was generated by

``urlquote()`` in the second example was not double-quoted when passed to

``iri_to_uri()``. This is a very important and useful feature. It means that

you can construct your IRI without worrying about whether it contains

non-ASCII characters and then, right at the end, call ``iri_to_uri()`` on the

result.

The ``iri_to_uri()`` function is also idempotent, which means the following is

always true::

    iri_to_uri(iri_to_uri(some_string)) = iri_to_uri(some_string)

So you can safely call it multiple times on the same IRI without risking

double-quoting problems.

.. _URI: http://www.ietf.org/rfc/rfc2396.txt

.. _IRI: http://www.ietf.org/rfc/rfc3987.txt

.. _RFC 3987: IRI_

Models

======

Because all strings are returned from the database as Unicode strings, model

fields that are character based (CharField, TextField, URLField, etc) will

contain Unicode values when Django retrieves data from the database. This

is *always* the case, even if the data could fit into an ASCII bytestring.

You can pass in bytestrings when creating a model or populating a field, and

Django will convert it to Unicode when it needs to.

Choosing between ``__str__()`` and ``__unicode__()``

----------------------------------------------------

One consequence of using Unicode by default is that you have to take some care

when printing data from the model.

In particular, rather than giving your model a ``__str__()`` method, we

recommended you implement a ``__unicode__()`` method. In the ``__unicode__()``

method, you can quite safely return the values of all your fields without

having to worry about whether they fit into a bytestring or not. (The way

Python works, the result of ``__str__()`` is *always* a bytestring, even if you

accidentally try to return a Unicode object).

You can still create a ``__str__()`` method on your models if you want, of

course, but you shouldn't need to do this unless you have a good reason.

Django's ``Model`` base class automatically provides a ``__str__()``

implementation that calls ``__unicode__()`` and encodes the result into UTF-8.

This means you'll normally only need to implement a ``__unicode__()`` method

and let Django handle the coercion to a bytestring when required.

Taking care in ``get_absolute_url()``

-------------------------------------

URLs can only contain ASCII characters. If you're constructing a URL from

pieces of data that might be non-ASCII, be careful to encode the results in a

way that is suitable for a URL. The ``django.db.models.permalink()`` decorator

handles this for you automatically.

If you're constructing a URL manually (i.e., *not* using the ``permalink()``

decorator), you'll need to take care of the encoding yourself. In this case,

use the ``iri_to_uri()`` and ``urlquote()`` functions that were documented

above_. For example::

    from django.utils.encoding import iri_to_uri

    from django.utils.http import urlquote

    def get_absolute_url(self):

        url = u'/person/%s/?x=0&y=0' % urlquote(self.location)

        return iri_to_uri(url)

This function returns a correctly encoded URL even if ``self.location`` is

something like "Jack visited Paris & Orléans". (In fact, the ``iri_to_uri()``

call isn't strictly necessary in the above example, because all the

non-ASCII characters would have been removed in quoting in the first line.)

.. _above: `URI and IRI handling`_

The database API

================

You can pass either Unicode strings or UTF-8 bytestrings as arguments to

``filter()`` methods and the like in the database API. The following two

querysets are identical::

    qs = People.objects.filter(name__contains=u'Å')

    qs = People.objects.filter(name__contains='\xc3\x85') # UTF-8 encoding of Å

Templates

=========

You can use either Unicode or bytestrings when creating templates manually::

	from django.template import Template

	t1 = Template('This is a bytestring template.')

	t2 = Template(u'This is a Unicode template.')

But the common case is to read templates from the filesystem, and this creates

a slight complication: not all filesystems store their data encoded as UTF-8.

If your template files are not stored with a UTF-8 encoding, set the :setting:`FILE_CHARSET`

setting to the encoding of the files on disk. When Django reads in a template

file, it will convert the data from this encoding to Unicode. (:setting:`FILE_CHARSET`

is set to ``'utf-8'`` by default.)

The :setting:`DEFAULT_CHARSET` setting controls the encoding of rendered templates.

This is set to UTF-8 by default.

Template tags and filters

-------------------------

A couple of tips to remember when writing your own template tags and filters:

    * Always return Unicode strings from a template tag's ``render()`` method

      and from template filters.

    * Use ``force_unicode()`` in preference to ``smart_unicode()`` in these

      places. Tag rendering and filter calls occur as the template is being

      rendered, so there is no advantage to postponing the conversion of lazy

      translation objects into strings. It's easier to work solely with Unicode

      strings at that point.

E-mail

======

Django's e-mail framework (in ``django.core.mail``) supports Unicode

transparently. You can use Unicode data in the message bodies and any headers.

However, you're still obligated to respect the requirements of the e-mail

specifications, so, for example, e-mail addresses should use only ASCII

characters.

The following code example demonstrates that everything except e-mail addresses

can be non-ASCII::

    from django.core.mail import EmailMessage

    subject = u'My visit to Sør-Trøndelag'

    sender = u'Arnbjörg Ráðormsdóttir <arnbjorg@example.com>'

    recipients = ['Fred <fred@example.com']

    body = u'...'

    EmailMessage(subject, body, sender, recipients).send()

Form submission

===============

HTML form submission is a tricky area. There's no guarantee that the

submission will include encoding information, which means the framework might

have to guess at the encoding of submitted data.

Django adopts a "lazy" approach to decoding form data. The data in an

``HttpRequest`` object is only decoded when you access it. In fact, most of

the data is not decoded at all. Only the ``HttpRequest.GET`` and

``HttpRequest.POST`` data structures have any decoding applied to them. Those

two fields will return their members as Unicode data. All other attributes and

methods of ``HttpRequest`` return data exactly as it was submitted by the

client.

By default, the :setting:`DEFAULT_CHARSET` setting is used as the assumed encoding

for form data. If you need to change this for a particular form, you can set

the ``encoding`` attribute on an ``HttpRequest`` instance. For example::

    def some_view(request):

        # We know that the data must be encoded as KOI8-R (for some reason).

        request.encoding = 'koi8-r'

        ...

You can even change the encoding after having accessed ``request.GET`` or

``request.POST``, and all subsequent accesses will use the new encoding.

Most developers won't need to worry about changing form encoding, but this is

a useful feature for applications that talk to legacy systems whose encoding

you cannot control.

Django does not decode the data of file uploads, because that data is normally

treated as collections of bytes, rather than strings. Any automatic decoding

there would alter the meaning of the stream of bytes.