Django2.0手册:Django Utils

This document covers all stable modules in django.utils. Most of the
modules in django.utils are designed for internal use and only the
following parts can be considered stable and thus backwards compatible as per
the internal release deprecation policy.


This module contains helper functions for controlling caching. It does so by
managing the Vary header of responses. It includes functions to patch the
header of response objects directly and decorators that change functions to do
that header-patching themselves.

For information on the Vary header, see RFC 7231#section-7.1.4.

Essentially, the Vary HTTP header defines which headers a cache should take
into account when building its cache key. Requests with the same path but
different header content for headers named in Vary need to get different
cache keys to prevent delivery of wrong content.

For example, internationalization middleware would
need to distinguish caches by the Accept-language header.

patch_cache_control(response, **kwargs)[source]

This function patches the Cache-Control header by adding all keyword
arguments to it. The transformation is as follows:

  • All keyword parameter names are turned to lowercase, and underscores
    are converted to hyphens.
  • If the value of a parameter is True (exactly True, not just a
    true value), only the parameter name is added to the header.
  • All other parameters are added with their value, after applying
    str() to it.

Returns the max-age from the response Cache-Control header as an integer
(or None if it wasn’t found or wasn’t an integer).

patch_response_headers(response, cache_timeout=None)[source]

Adds some useful headers to the given HttpResponse object:

  • ETag
  • Expires
  • Cache-Control

Each header is only added if it isn’t already set.

cache_timeout is in seconds. The CACHE_MIDDLEWARE_SECONDS
setting is used by default.

Changed in Django 1.11:

In older versions, the Last-Modified header was also set.

Deprecated since version 1.11: Since the USE_ETAGS setting is deprecated, this function won’t set
the ETag header when the deprecation ends in Django 2.1.


Adds a Cache-Control: max-age=0, no-cache, no-store, must-revalidate
header to a response to indicate that a page should never be cached.

patch_vary_headers(response, newheaders)[source]

Adds (or updates) the Vary header in the given HttpResponse object.
newheaders is a list of header names that should be in Vary.
Existing headers in Vary aren’t removed.

get_cache_key(request, key_prefix=None)[source]

Returns a cache key based on the request path. It can be used in the
request phase because it pulls the list of headers to take into account
from the global path registry and uses those to build a cache key to
check against.

If there is no headerlist stored, the page needs to be rebuilt, so this
function returns None.

learn_cache_key(request, response, cache_timeout=None, key_prefix=None)[source]

Learns what headers to take into account for some request path from the
response object. It stores those headers in a global path registry so that
later access to that path will know what headers to take into account
without building the response object itself. The headers are named in
the Vary header of the response, but we want to prevent response

The list of headers to use for cache key generation is stored in the same
cache as the pages themselves. If the cache ages some data out of the
cache, this just means that we have to build the response once to get at
the Vary header and so at the list of headers to use for the cache key.


The functions defined in this module share the following properties:

  • They raise ValueError if their input is well formatted but isn’t a
    valid date or time.
  • They return None if it isn’t well formatted at all.
  • They accept up to picosecond resolution in input, but they truncate it to
    microseconds, since that’s what Python supports.

Parses a string and returns a


Parses a string and returns a datetime.time.

UTC offsets aren’t supported; if value describes one, the result is


Parses a string and returns a datetime.datetime.

UTC offsets are supported; if value describes one, the result’s
tzinfo attribute is a FixedOffset


Parses a string and returns a datetime.timedelta.

Expects data in the format "DD HH:MM:SS.uuuuuu" or as specified by ISO
8601 (e.g. P4DT1H15M20S which is equivalent to 4 1:15:20) or
PostgreSQL’s day-time interval format (e.g. 3 days 04:05:06).

Changed in Django 2.0:

Support for PostgreSQL’s interval format was added.


method_decorator(decorator, name=”)[source]

Converts a function decorator into a method decorator. It can be used to
decorate methods or classes; in the latter case, name is the name
of the method to be decorated and is required.

decorator may also be a list or tuple of functions. They are wrapped
in reverse order so that the call order is the order in which the functions
appear in the list/tuple.

See decorating class based views for
example usage.


Given a middleware class, returns a view decorator. This lets you use
middleware functionality on a per-view basis. The middleware is created
with no params passed.

It assumes middleware that’s compatible with the old style of Django 1.9
and earlier (having methods like process_request(),
process_exception(), and process_response()).


Like decorator_from_middleware, but returns a function
that accepts the arguments to be passed to the middleware_class.
For example, the cache_page()
decorator is created from the CacheMiddleware like this:

cache_page = decorator_from_middleware_with_args(CacheMiddleware)

def my_view(request):



A decorator that defines __unicode__ and __str__ methods under
Python 2. Under Python 3 it does nothing.

To support Python 2 and 3 with a single code base, define a __str__
method returning text (use six.text_type() if you’re doing some
casting) and apply this decorator to the class.

smart_text(s, encoding=’utf-8′, strings_only=False, errors=’strict’)[source]

Returns a str object representing s. Treats bytestrings using the
encoding codec.

If strings_only is True, don’t convert (some) non-string-like


Determine if the object instance is of a protected type.

Objects of protected types are preserved as-is when passed to

force_text(s, encoding=’utf-8′, strings_only=False, errors=’strict’)[source]

Similar to smart_text, except that lazy instances are resolved to
strings, rather than kept as lazy objects.

If strings_only is True, don’t convert (some) non-string-like

smart_bytes(s, encoding=’utf-8′, strings_only=False, errors=’strict’)[source]

Returns a bytestring version of s, encoded as specified in

If strings_only is True, don’t convert (some) non-string-like

force_bytes(s, encoding=’utf-8′, strings_only=False, errors=’strict’)[source]

Similar to smart_bytes, except that lazy instances are resolved to
bytestrings, rather than kept as lazy objects.

If strings_only is True, don’t convert (some) non-string-like

smart_str(s, encoding=’utf-8′, strings_only=False, errors=’strict’)

Alias of smart_text(). This function returns a str or a lazy

For instance, this is suitable for writing to sys.stdout.

Alias of smart_bytes() on Python 2 (in older versions of Django that
support it).

force_str(s, encoding=’utf-8′, strings_only=False, errors=’strict’)

Alias of force_text(). This function always returns a str.

Alias of force_bytes() on Python 2 (in older versions of Django that
support it).


Convert an Internationalized Resource Identifier (IRI) portion to a URI
portion that is suitable for inclusion in a URL.

This is the algorithm from section 3.1 of RFC 3987#section-3.1, slightly
simplified since the input is assumed to be a string rather than an
arbitrary byte stream.

Takes an IRI (string or UTF-8 bytes) and returns a string containing the
encoded result.


Converts a Uniform Resource Identifier into an Internationalized Resource

This is an algorithm from section 3.2 of RFC 3987#section-3.2.

Takes a URI in ASCII bytes and returns a string containing the encoded


Convert a file system path to a URI portion that is suitable for inclusion
in a URL. The path is assumed to be either UTF-8 bytes or string.

This method will encode certain characters that would normally be
recognized as special characters for URIs. Note that this method does not
encode the ‘ character, as it is a valid character within URIs. See
encodeURIComponent() JavaScript function for more details.

Returns an ASCII string containing the encoded result.


Escapes the unsafe characters from the path portion of a Uniform Resource
Identifier (URI).


Sample usage:

>>> from django.utils import feedgenerator
>>> feed = feedgenerator.Rss201rev2Feed(
...     title="Poynter E-Media Tidbits",
...     link="",
...     description="A group Weblog by the sharpest minds in online media/journalism/publishing.",
...     language="en",
... )
>>> feed.add_item(
...     title="Hello",
...     link="",
...     description="Testing.",
... )
>>> with open('test.rss', 'w') as fp:
...     feed.write(fp, 'utf-8')

For simplifying the selection of a generator use feedgenerator.DefaultFeed
which is currently Rss201rev2Feed

For definitions of the different versions of RSS, see:

get_tag_uri(url, date)[source]

Creates a TagURI.



class SyndicationFeed[source]

Base class for all syndication feeds. Subclasses should provide write().

__init__(title, link, description, language=None, author_email=None, author_name=None, author_link=None, subtitle=None, categories=None, feed_url=None, feed_copyright=None, feed_guid=None, ttl=None, **kwargs)[source]

Initialize the feed with the given dictionary of metadata, which applies
to the entire feed.

Any extra keyword arguments you pass to __init__ will be stored in

All parameters should be strings, except categories, which should
be a sequence of strings.

add_item(title, link, description, author_email=None, author_name=None, author_link=None, pubdate=None, comments=None, unique_id=None, categories=(), item_copyright=None, ttl=None, updateddate=None, enclosures=None, **kwargs)[source]

Adds an item to the feed. All args are expected to be strings except
pubdate and updateddate, which are datetime.datetime
objects, and enclosures, which is a list of Enclosure instances.


Return extra attributes to place on the root (i.e. feed/channel)
element. Called from write().


Add elements in the root (i.e. feed/channel) element.
Called from write().


Return extra attributes to place on each item (i.e. item/entry)

add_item_elements(handler, item)[source]

Add elements on each item (i.e. item/entry) element.

write(outfile, encoding)[source]

Outputs the feed in the given encoding to outfile, which is a
file-like object. Subclasses should override this.


Returns the feed in the given encoding as a string.


Returns the latest pubdate or updateddate for all items in the
feed. If no items have either of these attributes this returns the
current UTC date/time.

Changed in Django 1.11:

In older versions, it returned the current date/time without any
timezone information.


class Enclosure[source]

Represents an RSS enclosure


class RssFeed(SyndicationFeed)[source]


class Rss201rev2Feed(RssFeed)[source]



class RssUserland091Feed(RssFeed)[source]



class Atom1Feed(SyndicationFeed)[source]



class cached_property(func, name=None)[source]

The @cached_property decorator caches the result of a method with a
single self argument as a property. The cached result will persist
as long as the instance does, so if the instance is passed around and the
function subsequently invoked, the cached result will be returned.

Consider a typical case, where a view might need to call a model’s method
to perform some computation, before placing the model instance into the
context, where the template might invoke the method once more:

# the model
class Person(models.Model):

    def friends(self):
        # expensive computation
        return friends

# in the view:
if person.friends():

And in the template you would have:

{% for friend in person.friends %}

Here, friends() will be called twice. Since the instance person in
the view and the template are the same, decorating the friends() method
with @cached_property can avoid that:

from django.utils.functional import cached_property

class Person(models.Model):

    def friends(self):

Note that as the method is now a property, in Python code it will need to
be invoked appropriately:

# in the view:
if person.friends:

The cached value can be treated like an ordinary attribute of the instance:

# clear it, requiring re-computation next time it's called
del person.friends # or delattr(person, "friends")

# set a value manually, that will persist on the instance until cleared
person.friends = ["Huckleberry Finn", "Tom Sawyer"]

As well as offering potential performance advantages, @cached_property
can ensure that an attribute’s value does not change unexpectedly over the
life of an instance. This could occur with a method whose computation is
based on, or simply if a change were saved to the
database by some other process in the brief interval between subsequent
invocations of a method on the same instance.

You can use the name argument to make cached properties of other
methods. For example, if you had an expensive get_friends() method and
wanted to allow calling it without retrieving the cached value, you could

friends = cached_property(get_friends, name='friends')

While person.get_friends() will recompute the friends on each call, the
value of the cached property will persist until you delete it as described

x = person.friends         # calls first time
y = person.get_friends()   # calls again
z = person.friends         # does not call
x is z                     # is True
keep_lazy(func, *resultclasses)[source]

Django offers many utility functions (particularly in django.utils)
that take a string as their first argument and do something to that string.
These functions are used by template filters as well as directly in other

If you write your own similar functions and deal with translations, you’ll
face the problem of what to do when the first argument is a lazy
translation object. You don’t want to convert it to a string immediately,
because you might be using this function outside of a view (and hence the
current thread’s locale setting will not be correct).

For cases like this, use the django.utils.functional.keep_lazy()
decorator. It modifies the function so that if it’s called with a lazy
translation as one of its arguments, the function evaluation is delayed
until it needs to be converted to a string.

For example:

from django.utils.functional import keep_lazy, keep_lazy_text

def fancy_utility_function(s, ...):
    # Do some conversion on string 's'
fancy_utility_function = keep_lazy(str)(fancy_utility_function)

# Or more succinctly:
def fancy_utility_function(s, ...):

The keep_lazy() decorator takes a number of extra arguments (*args)
specifying the type(s) that the original function can return. A common
use case is to have functions that return text. For these, you can just
pass the str type to keep_lazy (or even simpler, use the
keep_lazy_text() decorator described in the next section).

Using this decorator means you can write your function and assume that the
input is a proper string, then add support for lazy translation objects at
the end.


A shortcut for keep_lazy(str)(func).

If you have a function that returns text and you want to be able to take
lazy arguments while delaying their evaluation, simply use this decorator:

from django.utils.functional import keep_lazy, keep_lazy_text

# Our previous example was:
def fancy_utility_function(s, ...):

# Which can be rewritten as:
def fancy_utility_function(s, ...):


Usually you should build up HTML using Django’s templates to make use of its
autoescape mechanism, using the utilities in django.utils.safestring
where appropriate. This module provides some additional low level utilities for
escaping HTML.


Returns the given text with ampersands, quotes and angle brackets encoded
for use in HTML. The input is first passed through
force_text() and the output has
mark_safe() applied.


Similar to escape(), except that it doesn’t operate on pre-escaped
strings, so it will not double escape.

format_html(format_string, *args, **kwargs)[source]

This is similar to str.format(), except that it is appropriate for
building up HTML fragments. All args and kwargs are passed through
conditional_escape() before being passed to str.format().

For the case of building up small HTML fragments, this function is to be
preferred over string interpolation using % or str.format()
directly, because it applies escaping to all arguments – just like the
template system applies escaping by default.

So, instead of writing:

mark_safe("%s <b>%s</b> %s" % (

You should instead use:

format_html("{} <b>{}</b> {}",

This has the advantage that you don’t need to apply escape() to each
argument and risk a bug and an XSS vulnerability if you forget one.

Note that although this function uses str.format() to do the
interpolation, some of the formatting options provided by str.format()
(e.g. number formatting) will not work, since all arguments are passed
through conditional_escape() which (ultimately) calls
force_text() on the values.

format_html_join(sep, format_string, args_generator)[source]

A wrapper of format_html(), for the common case of a group of
arguments that need to be formatted using the same format string, and then
joined using sep. sep is also passed through

args_generator should be an iterator that returns the sequence of
args that will be passed to format_html(). For example:

    '\n', "<li>{} {}</li>",
    ((u.first_name, u.last_name) for u in users)

Tries to remove anything that looks like an HTML tag from the string, that
is anything contained within <>.

Absolutely NO guarantee is provided about the resulting string being
HTML safe. So NEVER mark safe the result of a strip_tag call without
escaping it first, for example with escape().

For example:


If value is "<b>Joel</b> <button>is</button> a <span>slug</span>"
the return value will be "Joel is a slug".

If you are looking for a more robust solution, take a look at the bleach Python library.


The __html__() method on a class helps non-Django templates detect
classes whose output doesn’t require HTML escaping.

This decorator defines the __html__() method on the decorated class
by wrapping __str__() in mark_safe().
Ensure the __str__() method does indeed return text that doesn’t
require HTML escaping.


urlencode(query, doseq=False)[source]

A version of Python’s urllib.parse.urlencode() function that can
operate on MultiValueDict and non-string values.


Formats the time to ensure compatibility with Netscape’s cookie standard.

Accepts a floating point number expressed in seconds since the epoch in
UTC–such as that outputted by time.time(). If set to None,
defaults to the current time.

Outputs a string in the format Wdy, DD-Mon-YYYY HH:MM:SS GMT.


Formats the time to match the RFC 1123 date format as specified by HTTP
RFC 7231#section-

Accepts a floating point number expressed in seconds since the epoch in
UTC–such as that outputted by time.time(). If set to None,
defaults to the current time.

Outputs a string in the format Wdy, DD Mon YYYY HH:MM:SS GMT.


Converts a base 36 string to an integer.


Converts a positive integer to a base 36 string.


Encodes a bytestring in base64 for use in URLs, stripping any trailing
equal signs.


Decodes a base64 encoded string, adding back any trailing equal signs that
might have been stripped.


Functions for working with Python modules.


Imports a dotted module path and returns the attribute/class designated by
the last name in the path. Raises ImportError if the import failed. For

from django.utils.module_loading import import_string
ValidationError = import_string('django.core.exceptions.ValidationError')

is equivalent to:

from django.core.exceptions import ValidationError


Functions and classes for working with “safe strings”: strings that can be
displayed safely without further escaping in HTML. Marking something as a “safe
string” means that the producer of the string has already turned characters
that should not be interpreted by the HTML engine (e.g. ‘<‘) into the
appropriate entities.

class SafeString

A str subclass that has been specifically marked as “safe”
(requires no further escaping) for HTML output purposes. Alias of

class SafeText[source]

A str subclass that has been specifically marked as “safe” for HTML
output purposes.


Explicitly mark a string as safe for (HTML) output purposes. The returned
object can be used everywhere a string is appropriate.

Can be called multiple times on a single string.

Can also be used as a decorator.

For building up fragments of HTML, you should normally be using
django.utils.html.format_html() instead.

String marked safe will become unsafe again if modified. For example:

>>> mystr = '<b>Hello World</b>   '
>>> mystr = mark_safe(mystr)
>>> type(mystr)
<class 'django.utils.safestring.SafeText'>

>>> mystr = mystr.strip()  # removing whitespace
>>> type(mystr)
<type 'str'>
Changed in Django 1.11:

Added support for decorator usage.


format_lazy(format_string, *args, **kwargs)
New in Django 1.11.

A version of str.format() for when format_string, args,
and/or kwargs contain lazy objects. The first argument is the string to
be formatted. For example:

from django.utils.text import format_lazy
from django.utils.translation import pgettext_lazy

urlpatterns = [
    path(format_lazy('{person}/<int:pk>/', person=pgettext_lazy('URL', 'person')),

This example allows translators to translate part of the URL. If “person”
is translated to “persona”, the regular expression will match
persona/(?P<pk>\d+)/$, e.g. persona/5/.


Converts to ASCII if allow_unicode is False (default). Converts spaces to
hyphens. Removes characters that aren’t alphanumerics, underscores, or
hyphens. Converts to lowercase. Also strips leading and trailing whitespace.

For example:


If value is "Joel is a slug", the output will be

You can set the allow_unicode parameter to True, if you want to
allow Unicode characters:

slugify(value, allow_unicode=True)

If value is "你好 World", the output will be "你好-world".



tzinfo instance that represents UTC.

class FixedOffset(offset=None, name=None)[source]

A tzinfo subclass modeling a fixed offset from UTC.
offset is an integer number of minutes east of UTC.


Returns a tzinfo instance that represents a time zone
with a fixed offset from UTC.

offset is a datetime.timedelta or an integer number of
minutes. Use positive values for time zones east of UTC and negative
values for west of UTC.


Returns a tzinfo instance that represents the
default time zone.


Returns the name of the default time zone.


Returns a tzinfo instance that represents the
current time zone.


Returns the name of the current time zone.


Sets the current time zone. The
timezone argument must be an instance of a tzinfo
subclass or a time zone name.


Unsets the current time zone.


This is a Python context manager that sets the current time zone on entry with activate(), and restores
the previously active time zone on exit. If the timezone argument is
None, the current time zone is unset
on entry with deactivate() instead.

override is also usable as a function decorator.

localtime(value=None, timezone=None)[source]

Converts an aware datetime to a different time zone,
by default the current time zone.

When value is omitted, it defaults to now().

This function doesn’t work on naive datetimes; use make_aware()

Changed in Django 1.11:

In older versions, value is a required argument.

localdate(value=None, timezone=None)[source]
New in Django 1.11.

Uses localtime() to convert an aware datetime to a
date() in a different time zone, by default the
current time zone.

When value is omitted, it defaults to now().

This function doesn’t work on naive datetimes.


Returns a datetime that represents the
current point in time. Exactly what’s returned depends on the value of

  • If USE_TZ is False, this will be a
    naive datetime (i.e. a datetime
    without an associated timezone) that represents the current time
    in the system’s local timezone.
  • If USE_TZ is True, this will be an
    aware datetime representing the
    current time in UTC. Note that now() will always return
    times in UTC regardless of the value of TIME_ZONE;
    you can use localtime() to get the time in the current time zone.

Returns True if value is aware, False if it is naive. This
function assumes that value is a datetime.


Returns True if value is naive, False if it is aware. This
function assumes that value is a datetime.

make_aware(value, timezone=None, is_dst=None)[source]

Returns an aware datetime that represents the same
point in time as value in timezone, value being a naive
datetime. If timezone is set to None, it
defaults to the current time zone.

The pytz.AmbiguousTimeError exception is raised if you try to make
value aware during a DST transition where the same time occurs twice
(when reverting from DST). Setting is_dst to True or False will
avoid the exception by choosing if the time is pre-transition or
post-transition respectively.

The pytz.NonExistentTimeError exception is raised if you try to make
value aware during a DST transition such that the time never occurred
(when entering into DST). Setting is_dst to True or False will
avoid the exception by moving the hour backwards or forwards by 1
respectively. For example, is_dst=True would change a nonexistent
time of 2:30 to 1:30 and is_dst=False would change the time to 3:30.

make_naive(value, timezone=None)[source]

Returns a naive datetime that represents in
timezone the same point in time as value, value being an
aware datetime. If timezone is set to None, it
defaults to the current time zone.


For a complete discussion on the usage of the following see the
translation documentation.

The u prefix on the functions below comes from a difference in Python 2
between unicode and bytestrings. If your code doesn’t support Python 2, use the
functions without the u.


Translates message and returns it as a string.

pgettext(context, message)[source]

Translates message given the context and returns it as a string.

For more information, see Contextual markers.

pgettext_lazy(context, message)

Same as the non-lazy versions above, but using lazy execution.

See lazy translations documentation.


Marks strings for translation but doesn’t translate them now. This can be
used to store strings in global variables that should stay in the base
language (because they might be used externally) and will be translated

ngettext(singular, plural, number)[source]
ungettext(singular, plural, number)

Translates singular and plural and returns the appropriate string
based on number.

npgettext(context, singular, plural, number)[source]

Translates singular and plural and returns the appropriate string
based on number and the context.

ngettext_lazy(singular, plural, number)[source]
ungettext_lazy(singular, plural, number)
npgettext_lazy(context, singular, plural, number)[source]

Same as the non-lazy versions above, but using lazy execution.

See lazy translations documentation.


Deprecated since version 1.11: Use django.utils.text.format_lazy() instead.
string_concat(*strings) can be replaced by
format_lazy('{}' * len(strings), *strings).

Lazy variant of string concatenation, needed for translations that are
constructed from multiple parts.


Fetches the translation object for a given language and activates it as
the current translation object for the current thread.


Deactivates the currently active translation object so that further _ calls
will resolve against the default translation object, again.


Makes the active translation object a NullTranslations() instance.
This is useful when we want delayed translations to appear as the original
string for some reason.

override(language, deactivate=False)[source]

A Python context manager that uses
django.utils.translation.activate() to fetch the translation object
for a given language, activates it as the translation object for the
current thread and reactivates the previous active language on exit.
Optionally, it can simply deactivate the temporary translation on exit with
django.utils.translation.deactivate() if the deactivate argument
is True. If you pass None as the language argument, a
NullTranslations() instance is activated within the context.

override is also usable as a function decorator.


Checks whether there is a global language file for the given language
code (e.g. ‘fr’, ‘pt_BR’). This is used to decide whether a user-provided
language is available.


Returns the currently selected language code. Returns None if
translations are temporarily deactivated (by deactivate_all() or
when None is passed to override()).


Returns selected language’s BiDi layout:

  • False = left-to-right layout
  • True = right-to-left layout
get_language_from_request(request, check_path=False)[source]

Analyzes the request to find what language the user wants the system to
show. Only languages listed in settings.LANGUAGES are taken into account.
If the user requests a sublanguage where we have a main language, we send
out the main language.

If check_path is True, the function first checks the requested URL
for whether its path begins with a language code listed in the
LANGUAGES setting.


Turns a language name (en-us) into a locale name (en_US).


Turns a Django template into something that is understood by xgettext.
It does so by translating the Django translation tags into standard
gettext function invocations.


Session key under which the active language for the current session is