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

Unicode data

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

Django supports Unicode data everywhere.

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`_ for details on how to set or alter

  the database character set encoding.

* PostgreSQL users, refer to the `PostgreSQL manual`_ for details on creating

  databases with the correct encoding.

* Oracle users, refer to the `Oracle manual`_ for details on how to set

  (`section 2`_) or alter (`section 11`_) the database character set encoding.

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

  for internal encoding.

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

.. _PostgreSQL manual: https://www.postgresql.org/docs/current/multibyte.html#id-1.6.11.5.6

.. _Oracle manual: https://docs.oracle.com/en/database/oracle/oracle-database/21/nlspg/index.html

.. _section 2: https://docs.oracle.com/en/database/oracle/oracle-database/21/nlspg/choosing-character-set.html

.. _section 11: https://docs.oracle.com/en/database/oracle/oracle-database/21/nlspg/character-set-migration.html

All of Django's database backends automatically convert strings into

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

convert strings retrieved from the database into 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 normal strings or bytestrings (starting with a 'b').

.. 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 email). 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

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

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

Translated strings

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

Aside from 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 ``str()`` with the lazy translation as the argument will generate a

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 string 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 strings and bytestrings.

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

  converts its input to a 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 ``str()`` function for its error

  handling.

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

  identical to ``smart_str()`` in almost all cases. The difference is when the

  first argument is a :ref:`lazy translation <lazy-translations>` instance.

  While ``smart_str()`` preserves lazy translations, ``force_str()`` forces

  those objects to a string (causing the translation to occur). Normally,

  you'll want to use ``smart_str()``. However, ``force_str()`` 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_bytes(s, encoding='utf-8', strings_only=False, errors='strict')``

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

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

  behavior as for ``smart_str()`` and ``force_str()``. 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 ``force_str()``. Call it as early as

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

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

.. _uri-and-iri-handling:

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 :rfc:`IRI <3987>` -- very loosely speaking, a :rfc:`URI <2396>`

that can contain Unicode characters. Use these functions for quoting and

converting an IRI to a URI:

* The :func:`django.utils.encoding.iri_to_uri()` function, which implements the

  conversion from IRI to URI as required by :rfc:`3987#section-3.1`.

* The :func:`urllib.parse.quote` and :func:`urllib.parse.quote_plus`

  functions from Python's standard library.

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

important to keep them straight. Normally, you would use ``quote()`` 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::

    >>> from urllib.parse import quote

    >>> from django.utils.encoding import iri_to_uri

    >>> quote('Paris & Orléans')

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

    >>> iri_to_uri('/favorites/François/%s' % quote('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

``quote()`` 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.

Similarly, Django provides :func:`django.utils.encoding.uri_to_iri()` which

implements the conversion from URI to IRI as per :rfc:`3987#section-3.2`.

An example to demonstrate::

    >>> from django.utils.encoding import uri_to_iri

    >>> uri_to_iri('/%E2%99%A5%E2%99%A5/?utf8=%E2%9C%93')

    '/♥♥/?utf8=✓'

    >>> uri_to_iri('%A9hello%3Fworld')

    '%A9hello%3Fworld'

In the first example, the UTF-8 characters are unquoted. In the second, the

percent-encodings remain unchanged because they lie outside the valid UTF-8

range or represent a reserved character.

Both ``iri_to_uri()`` and ``uri_to_iri()`` functions are idempotent, which means the

following is always true::

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

    uri_to_iri(uri_to_iri(some_string)) == uri_to_iri(some_string)

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

double-quoting problems.

Models

======

Because all strings are returned from the database as ``str`` objects, 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 strings when it needs to.

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 :func:`~django.urls.reverse` function

handles this for you automatically.

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

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

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

above_. For example::

    from urllib.parse import quote

    from django.utils.encoding import iri_to_uri

    def get_absolute_url(self):

        url = '/person/%s/?x=0&y=0' % quote(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`_

Templates

=========

Use strings when creating templates manually::

    from django.template import Template

    t2 = Template('This is a string template.')

But the common case is to read templates from the filesystem. If your template

files are not stored with a UTF-8 encoding, adjust the :setting:`TEMPLATES`

setting. The built-in :py:mod:`~django.template.backends.django` backend

provides the ``'file_charset'`` option to change the encoding used to read

files from disk.

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 strings from a template tag's ``render()`` method

  and from template filters.

* Use ``force_str()`` in preference to ``smart_str()`` 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

  strings at that point.

.. _unicode-files:

Files

=====

If you intend to allow users to upload files, you must ensure that the

environment used to run Django is configured to work with non-ASCII file names.

If your environment isn't configured correctly, you'll encounter

``UnicodeEncodeError`` exceptions when saving files with file names or content

that contains non-ASCII characters.

Filesystem support for UTF-8 file names varies and might depend on the

environment. Check your current configuration in an interactive Python shell by

running::

    import sys

    sys.getfilesystemencoding()

This should output "UTF-8".

The ``LANG`` environment variable is responsible for setting the expected

encoding on Unix platforms. Consult the documentation for your operating system

and application server for the appropriate syntax and location to set this

variable. See the :doc:`/howto/deployment/wsgi/modwsgi` for examples.

In your development environment, you might need to add a setting to your

``~.bashrc`` analogous to:::

    export LANG="en_US.UTF-8"

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.