Django natively supports Unicode data everywhere. Providing your database can somehow store the data, you can safely pass around 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.
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.
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.
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 DEFAULT_CHARSET setting is set
to something other than 'utf-8' you can use that other encoding in your
bytestrings! 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
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.
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 internationalization documentation.
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.
The django.utils.encoding module contains a few functions that are handy
for converting back and forth between strings and bytestrings.
smart_text(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_text(s, encoding='utf-8', strings_only=False,
errors='strict') is identical to smart_text() in almost all
cases. The difference is when the first argument is a lazy
translation instance. While smart_text()
preserves lazy translations, force_text() forces those objects to a
string (causing the translation to occur). Normally, you’ll want
to use smart_text(). However, force_text() 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_text(). It forces the first
argument to a bytestring. The strings_only parameter has the same
behavior as for smart_text() and force_text(). 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_text(). 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.
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. Use these functions for quoting and converting an IRI to a URI:
django.utils.encoding.iri_to_uri() function, which implements the
conversion from IRI to URI as required by RFC 3987#section-3.1.urllib.parse.quote() and 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 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.
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.
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 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.)
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, 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 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. (FILE_CHARSET
is set to 'utf-8' by default.)
The DEFAULT_CHARSET setting controls the encoding of rendered templates.
This is set to UTF-8 by default.
A couple of tips to remember when writing your own template tags and filters:
render() method
and from template filters.force_text() in preference to smart_text() 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.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 that
contain 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.
In your development environment, you might need to add a setting to your
~.bashrc analogous to::
export LANG="en_US.UTF-8"
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 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.
Oct 31, 2018