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

Django Utils

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

.. module:: django.utils

   :synopsis: Django's built-in utilities.

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 :ref:`internal release deprecation policy <internal-release-deprecation-policy>`.

``django.utils.cache``

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

.. module:: django.utils.cache

   :synopsis: Helper functions for controlling caching.

This module contains helper functions for controlling HTTP 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, :doc:`internationalization </topics/i18n/index>` middleware would

need to distinguish caches by the ``Accept-language`` header.

.. function:: patch_cache_control(response, **kwargs)

    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.

.. function:: get_max_age(response)

    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).

.. function:: patch_response_headers(response, cache_timeout=None)

    Adds some useful headers to the given ``HttpResponse`` object:

    * ``Expires``

    * ``Cache-Control``

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

    ``cache_timeout`` is in seconds. The :setting:`CACHE_MIDDLEWARE_SECONDS`

    setting is used by default.

.. function:: add_never_cache_headers(response)

    Adds an ``Expires`` header to the current date/time.

    Adds a ``Cache-Control: max-age=0, no-cache, no-store, must-revalidate,

    private`` header to a response to indicate that a page should never be

    cached.

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

.. function:: patch_vary_headers(response, newheaders)

    Adds (or updates) the ``Vary`` header in the given ``HttpResponse`` object.

    ``newheaders`` is a list of header names that should be in ``Vary``. If

    headers contains an asterisk, then ``Vary`` header will consist of a single

    asterisk ``'*'``, according to :rfc:`7231#section-7.1.4`. Otherwise,

    existing headers in ``Vary`` aren't removed.

.. function:: get_cache_key(request, key_prefix=None, method='GET', cache=None)

    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``.

.. function:: learn_cache_key(request, response, cache_timeout=None, key_prefix=None, cache=None)

    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

    generation.

    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 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.

``django.utils.dateparse``

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

.. module:: django.utils.dateparse

   :synopsis: Functions to parse strings to datetime objects.

The functions defined in this module share the following properties:

- They accept strings in ISO 8601 date/time formats (or some close

  alternatives) and return objects from the corresponding classes in Python's

  :mod:`datetime` module.

- They raise :exc:`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.

.. function:: parse_date(value)

    Parses a string and returns a :class:`datetime.date`.

.. function:: parse_time(value)

    Parses a string and returns a :class:`datetime.time`.

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

    ``None``.

.. function:: parse_datetime(value)

    Parses a string and returns a :class:`datetime.datetime`.

    UTC offsets are supported; if ``value`` describes one, the result's

    ``tzinfo`` attribute is a :class:`datetime.timezone` instance.

.. function:: parse_duration(value)

    Parses a string and returns a :class:`datetime.timedelta`.

    Expects data in the format ``"DD HH:MM:SS.uuuuuu"``,

    ``"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``).

``django.utils.decorators``

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

.. module:: django.utils.decorators

    :synopsis: Functions that help with creating decorators for views.

.. function:: method_decorator(decorator, name='')

    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 :ref:`decorating class based views <decorating-class-based-views>` for

    example usage.

.. function:: decorator_from_middleware(middleware_class)

    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()``).

.. function:: decorator_from_middleware_with_args(middleware_class)

    Like ``decorator_from_middleware``, but returns a function

    that accepts the arguments to be passed to the middleware_class.

    For example, the :func:`~django.views.decorators.cache.cache_page`

    decorator is created from the ``CacheMiddleware`` like this::

         cache_page = decorator_from_middleware_with_args(CacheMiddleware)

         @cache_page(3600)

         def my_view(request):

             pass

.. function:: sync_only_middleware(middleware)

    Marks a middleware as :ref:`synchronous-only <async-middleware>`. (The

    default in Django, but this allows you to future-proof if the default ever

    changes in a future release.)

.. function:: async_only_middleware(middleware)

    Marks a middleware as :ref:`asynchronous-only <async-middleware>`. Django

    will wrap it in an asynchronous event loop when it is called from the WSGI

    request path.

.. function:: sync_and_async_middleware(middleware)

    Marks a middleware as :ref:`sync and async compatible <async-middleware>`,

    this allows to avoid converting requests. You must implement detection of

    the current request type to use this decorator. See :ref:`asynchronous

    middleware documentation <async-middleware>` for details.

``django.utils.encoding``

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

.. module:: django.utils.encoding

   :synopsis: A series of helper functions to manage character encoding.

.. function:: smart_str(s, encoding='utf-8', strings_only=False, errors='strict')

    Returns a ``str`` object representing arbitrary object ``s``. Treats

    bytestrings using the ``encoding`` codec.

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

    objects.

.. function:: is_protected_type(obj)

    Determine if the object instance is of a protected type.

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

    ``force_str(strings_only=True)``.

.. function:: force_str(s, encoding='utf-8', strings_only=False, errors='strict')

    Similar to ``smart_str()``, 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

    objects.

.. function:: smart_bytes(s, encoding='utf-8', strings_only=False, errors='strict')

    Returns a bytestring version of arbitrary object ``s``, encoded as

    specified in ``encoding``.

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

    objects.

.. function:: force_bytes(s, encoding='utf-8', strings_only=False, errors='strict')

    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

    objects.

.. function:: iri_to_uri(iri)

    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.

.. function:: uri_to_iri(uri)

    Converts a Uniform Resource Identifier into an Internationalized Resource

    Identifier.

    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

    result.

.. function:: filepath_to_uri(path)

    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, string, or a

    :class:`~pathlib.Path`.

    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.

.. function:: escape_uri_path(path)

    Escapes the unsafe characters from the path portion of a Uniform Resource

    Identifier (URI).

``django.utils.feedgenerator``

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

.. module:: django.utils.feedgenerator

   :synopsis: Syndication feed generation library -- used for generating RSS, etc.

Sample usage::

    >>> from django.utils import feedgenerator

    >>> feed = feedgenerator.Rss201rev2Feed(

    ...     title="Poynter E-Media Tidbits",

    ...     link="http://www.poynter.org/column.asp?id=31",

    ...     description="A group blog by the sharpest minds in online media/journalism/publishing.",

    ...     language="en",

    ... )

    >>> feed.add_item(

    ...     title="Hello",

    ...     link="http://www.holovaty.com/test/",

    ...     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:

https://web.archive.org/web/20110718035220/http://diveintomark.org/archives/2004/02/04/incompatible-rss

.. function:: get_tag_uri(url, date)

    Creates a TagURI.

    See https://web.archive.org/web/20110514113830/http://diveintomark.org/archives/2004/05/28/howto-atom-id

``SyndicationFeed``

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

.. class:: SyndicationFeed

    Base class for all syndication feeds. Subclasses should provide

    ``write()``.

    .. method:: __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)

        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

        ``self.feed``.

        All parameters should be strings, except ``categories``, which should

        be a sequence of strings.

    .. method:: 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)

        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.

    .. method:: num_items()

    .. method:: root_attributes()

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

        element. Called from ``write()``.

    .. method:: add_root_elements(handler)

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

        Called from ``write()``.

    .. method:: item_attributes(item)

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

        element.

    .. method:: add_item_elements(handler, item)

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

    .. method:: write(outfile, encoding)

        Outputs the feed in the given encoding to ``outfile``, which is a

        file-like object. Subclasses should override this.

    .. method:: writeString(encoding)

        Returns the feed in the given encoding as a string.

    .. method:: latest_post_date()

        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.

``Enclosure``

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

.. class:: Enclosure

    Represents an RSS enclosure

``RssFeed``

-----------

.. class:: RssFeed(SyndicationFeed)

``Rss201rev2Feed``

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

.. class:: Rss201rev2Feed(RssFeed)

    Spec: https://cyber.harvard.edu/rss/rss.html

``RssUserland091Feed``

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

.. class:: RssUserland091Feed(RssFeed)

    Spec: http://backend.userland.com/rss091

``Atom1Feed``

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

.. class:: Atom1Feed(SyndicationFeed)

    Spec: :rfc:`4287`

``django.utils.functional``

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

.. module:: django.utils.functional

    :synopsis: Functional programming tools.

.. class:: cached_property(func, name=None)

    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:

    .. code-block:: html+django

        {% 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):

            @cached_property

            def friends(self):

                ...

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

    be accessed 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"]

    Because of the way the :py:ref:`descriptor protocol

    <descriptor-invocation>` works, using ``del`` (or ``delattr``) on a

    ``cached_property`` that hasn't been accessed raises ``AttributeError``.

    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 ``datetime.now()``, or 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 make cached properties of methods. For example, if you had an

    expensive ``get_friends()`` method and wanted to allow calling it without

    retrieving the cached value, you could write::

        friends = cached_property(get_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

    above::

        x = person.friends         # calls first time

        y = person.get_friends()   # calls again

        z = person.friends         # does not call

        x is z                     # is True

    .. deprecated:: 4.1

        The ``name`` parameter is deprecated and will be removed in Django 5.0

        as it's unnecessary as of Python 3.6.

.. class:: classproperty(method=None)

    Similar to :py:func:`@classmethod <classmethod>`, the ``@classproperty``

    decorator converts the result of a method with a single ``cls`` argument

    into a property that can be accessed directly from the class.

.. function:: keep_lazy(func, *resultclasses)

    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

    code.

    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:

        @keep_lazy(str)

        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 pass the

    ``str`` type to ``keep_lazy`` (or use the :func:`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.

.. function:: keep_lazy_text(func)

    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, you can use this

    decorator::

        from django.utils.functional import keep_lazy, keep_lazy_text

        # Our previous example was:

        @keep_lazy(str)

        def fancy_utility_function(s, ...):

            ...

        # Which can be rewritten as:

        @keep_lazy_text

        def fancy_utility_function(s, ...):

            ...

``django.utils.html``

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

.. module:: django.utils.html

   :synopsis: HTML helper functions

Usually you should build up HTML using Django's templates to make use of its

autoescape mechanism, using the utilities in :mod:`django.utils.safestring`

where appropriate. This module provides some additional low level utilities for

escaping HTML.

.. function:: escape(text)

    Returns the given text with ampersands, quotes and angle brackets encoded

    for use in HTML. The input is first coerced to a string and the output has

    :func:`~django.utils.safestring.mark_safe` applied.

.. function:: conditional_escape(text)

    Similar to ``escape()``, except that it doesn't operate on preescaped

    strings, so it will not double escape.

.. function:: format_html(format_string, *args, **kwargs)

    This is similar to :meth:`str.format`, except that it is appropriate for

    building up HTML fragments. All args and kwargs are passed through

    :func:`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" % (

            some_html,

            escape(some_text),

            escape(some_other_text),

        ))

    You should instead use::

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

            mark_safe(some_html),

            some_text,

            some_other_text,

        )

    This has the advantage that you don't need to apply :func:`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 :func:`conditional_escape` which (ultimately) calls

    :func:`~django.utils.encoding.force_str` on the values.

.. function:: format_html_join(sep, format_string, args_generator)

    A wrapper of :func:`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

    :func:`conditional_escape`.

    ``args_generator`` should be an iterator that returns the sequence of

    ``args`` that will be passed to :func:`format_html`. For example::

        format_html_join(

            '\n', "<li>{} {}</li>",

            ((u.first_name, u.last_name) for u in users)

        )

.. function:: json_script(value, element_id=None)

    Escapes all HTML/XML special characters with their Unicode escapes, so

    value is safe for use with JavaScript. Also wraps the escaped JSON in a

    ``<script>`` tag. If the ``element_id`` parameter is not ``None``, the

    ``<script>`` tag is given the passed id. For example::

        >> json_script({"hello": "world"}, element_id="hello-data")

        '<script id="hello-data" type="application/json">{"hello": "world"}</script>'

    .. versionchanged:: 4.1

        In older versions, the ``element_id`` argument was required.

.. function:: strip_tags(value)

    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 :func:`~django.utils.html.escape`.

    For example::

        strip_tags(value)

    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

    <https://pypi.org/project/bleach/>`_ Python library.

.. function:: html_safe()

    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 :meth:`~django.utils.safestring.mark_safe`.

    Ensure the ``__str__()`` method does indeed return text that doesn't

    require HTML escaping.

``django.utils.http``

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

.. module:: django.utils.http

   :synopsis: HTTP helper functions. (URL encoding, cookie handling, ...)

.. function:: urlencode(query, doseq=False)

    A version of Python's :func:`urllib.parse.urlencode` function that can

    operate on ``MultiValueDict`` and non-string values.

.. function:: http_date(epoch_seconds=None)

    Formats the time to match the :rfc:`1123#section-5.2.14` date format as

    specified by HTTP :rfc:`7231#section-7.1.1.1`.

    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``.

.. function:: base36_to_int(s)

    Converts a base 36 string to an integer.

.. function:: int_to_base36(i)

    Converts a positive integer to a base 36 string.

.. function:: urlsafe_base64_encode(s)

    Encodes a bytestring to a base64 string for use in URLs, stripping any

    trailing equal signs.

.. function::  urlsafe_base64_decode(s)

    Decodes a base64 encoded string, adding back any trailing equal signs that

    might have been stripped.

``django.utils.module_loading``

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

.. module:: django.utils.module_loading

   :synopsis: Functions for working with Python modules.

Functions for working with Python modules.

.. function:: import_string(dotted_path)

    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

    example::

        from django.utils.module_loading import import_string

        ValidationError = import_string('django.core.exceptions.ValidationError')

    is equivalent to::

        from django.core.exceptions import ValidationError

``django.utils.safestring``

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

.. module:: django.utils.safestring

   :synopsis: Functions and classes for working with strings that can be displayed safely without further escaping in HTML.

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.

.. function:: mark_safe(s)

    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

    :func:`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.SafeString'>

        >>> mystr = mystr.strip()  # removing whitespace

        >>> type(mystr)

        <type 'str'>

``django.utils.text``

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

.. module:: django.utils.text

    :synopsis: Text manipulation.

.. function:: format_lazy(format_string, *args, **kwargs)

    A version of :meth:`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')),

                 PersonDetailView.as_view()),

        ]

    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/``.

.. function:: slugify(value, allow_unicode=False)

    Converts a string to a URL slug by:

    #. Converting to ASCII if ``allow_unicode`` is ``False`` (the default).

    #. Converting to lowercase.

    #. Removing characters that aren't alphanumerics, underscores, hyphens, or

       whitespace.

    #. Replacing any whitespace or repeated dashes with single dashes.

    #. Removing leading and trailing whitespace, dashes, and underscores.

    For example::

        >>> slugify(' Joel is a slug ')

        'joel-is-a-slug'

    If you want to allow Unicode characters, pass ``allow_unicode=True``. For

    example::

        >>> slugify('你好 World', allow_unicode=True)

        '你好-world'

.. _time-zone-selection-functions:

``django.utils.timezone``

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

.. module:: django.utils.timezone

    :synopsis: Timezone support.

.. data:: utc

    :class:`~datetime.tzinfo` instance that represents UTC.

    .. deprecated:: 4.1

        This is an alias to :attr:`datetime.timezone.utc`. Use

        :attr:`datetime.timezone.utc` directly.

.. function:: get_fixed_timezone(offset)

    Returns a :class:`~datetime.tzinfo` instance that represents a time zone

    with a fixed offset from UTC.

    ``offset`` is a :class:`datetime.timedelta` or an integer number of

    minutes. Use positive values for time zones east of UTC and negative

    values for west of UTC.

.. function:: get_default_timezone()

    Returns a :class:`~datetime.tzinfo` instance that represents the

    :ref:`default time zone <default-current-time-zone>`.

.. function:: get_default_timezone_name()

    Returns the name of the :ref:`default time zone

    <default-current-time-zone>`.

.. function:: get_current_timezone()

    Returns a :class:`~datetime.tzinfo` instance that represents the

    :ref:`current time zone <default-current-time-zone>`.

.. function:: get_current_timezone_name()

    Returns the name of the :ref:`current time zone

    <default-current-time-zone>`.

.. function:: activate(timezone)

    Sets the :ref:`current time zone <default-current-time-zone>`. The

    ``timezone`` argument must be an instance of a :class:`~datetime.tzinfo`

    subclass or a time zone name.

.. function:: deactivate()

    Unsets the :ref:`current time zone <default-current-time-zone>`.

.. function:: override(timezone)

    This is a Python context manager that sets the :ref:`current time zone

    <default-current-time-zone>` on entry with :func:`activate()`, and restores

    the previously active time zone on exit. If the ``timezone`` argument is

    ``None``, the :ref:`current time zone <default-current-time-zone>` is unset

    on entry with :func:`deactivate()` instead.

    ``override`` is also usable as a function decorator.

.. function:: localtime(value=None, timezone=None)

    Converts an aware :class:`~datetime.datetime` to a different time zone,

    by default the :ref:`current time zone <default-current-time-zone>`.

    When ``value`` is omitted, it defaults to :func:`now`.

    This function doesn't work on naive datetimes; use :func:`make_aware`

    instead.

.. function:: localdate(value=None, timezone=None)

    Uses :func:`localtime` to convert an aware :class:`~datetime.datetime` to a

    :meth:`~datetime.datetime.date` in a different time zone, by default the

    :ref:`current time zone <default-current-time-zone>`.

    When ``value`` is omitted, it defaults to :func:`now`.

    This function doesn't work on naive datetimes.

.. function:: now()

    Returns a :class:`~datetime.datetime` that represents the

    current point in time. Exactly what's returned depends on the value of

    :setting:`USE_TZ`:

    * If :setting:`USE_TZ` is ``False``, this will be a

      :ref:`naive <naive_vs_aware_datetimes>` datetime (i.e. a datetime

      without an associated timezone) that represents the current time

      in the system's local timezone.

    * If :setting:`USE_TZ` is ``True``, this will be an

      :ref:`aware <naive_vs_aware_datetimes>` datetime representing the

      current time in UTC. Note that :func:`now` will always return

      times in UTC regardless of the value of :setting:`TIME_ZONE`;

      you can use :func:`localtime` to get the time in the current time zone.

.. function:: is_aware(value)

    Returns ``True`` if ``value`` is aware, ``False`` if it is naive. This

    function assumes that ``value`` is a :class:`~datetime.datetime`.

.. function:: is_naive(value)

    Returns ``True`` if ``value`` is naive, ``False`` if it is aware. This

    function assumes that ``value`` is a :class:`~datetime.datetime`.

.. function:: make_aware(value, timezone=None, is_dst=None)

    Returns an aware :class:`~datetime.datetime` that represents the same

    point in time as ``value`` in ``timezone``, ``value`` being a naive

    :class:`~datetime.datetime`. If ``timezone`` is set to ``None``, it

    defaults to the :ref:`current time zone <default-current-time-zone>`.

    .. deprecated:: 4.0

        When using ``pytz``, 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.

        When using ``pytz``, the ``pytz.NonExistentTimeError`` exception is

        raised if you try to make ``value`` aware during a DST transition such

        that the time never occurred. For example, if the 2:00 hour is skipped

        during a DST transition, trying to make 2:30 aware in that time zone

        will raise an exception. To avoid that you can use ``is_dst`` to

        specify how ``make_aware()`` should interpret such a nonexistent time.

        If ``is_dst=True`` then the above time would be interpreted as 2:30 DST

        time (equivalent to 1:30 local time). Conversely, if ``is_dst=False``

        the time would be interpreted as 2:30 standard time (equivalent to 3:30

        local time).

        The ``is_dst`` parameter has no effect when using non-``pytz`` timezone

        implementations.

        The ``is_dst`` parameter is deprecated and will be removed in Django

        5.0.

.. function:: make_naive(value, timezone=None)

    Returns a naive :class:`~datetime.datetime` that represents in

    ``timezone``  the same point in time as ``value``, ``value`` being an

    aware :class:`~datetime.datetime`. If ``timezone`` is set to ``None``, it

    defaults to the :ref:`current time zone <default-current-time-zone>`.

``django.utils.translation``

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

.. module:: django.utils.translation

   :synopsis: Internationalization support.

For a complete discussion on the usage of the following see the

:doc:`translation documentation </topics/i18n/translation>`.

.. function:: gettext(message)

    Translates ``message`` and returns it as a string.

.. function:: pgettext(context, message)

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

    For more information, see :ref:`contextual-markers`.

.. function:: gettext_lazy(message)

.. function:: pgettext_lazy(context, message)

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

    See :ref:`lazy translations documentation <lazy-translations>`.

.. function:: gettext_noop(message)

    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

    later.

.. function:: ngettext(singular, plural, number)

    Translates ``singular`` and ``plural`` and returns the appropriate string

    based on ``number``.

.. function:: npgettext(context, singular, plural, number)

    Translates ``singular`` and ``plural`` and returns the appropriate string

    based on ``number`` and the ``context``.

.. function:: ngettext_lazy(singular, plural, number)

.. function:: npgettext_lazy(context, singular, plural, number)

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

    See :ref:`lazy translations documentation <lazy-translations>`.

.. function:: activate(language)

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

    the current translation object for the current thread.

.. function:: deactivate()

    Deactivates the currently active translation object so that further _ calls

    will resolve against the default translation object, again.

.. function:: deactivate_all()

    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.

.. function:: override(language, deactivate=False)

    A Python context manager that uses

    :func:`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 deactivate the temporary translation on exit with

    :func:`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.

.. function:: check_for_language(lang_code)

    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.

.. function:: get_language()

    Returns the currently selected language code. Returns ``None`` if

    translations are temporarily deactivated (by :func:`deactivate_all()` or

    when ``None`` is passed to :func:`override()`).

.. function:: get_language_bidi()

    Returns selected language's BiDi layout:

    * ``False`` = left-to-right layout

    * ``True`` = right-to-left layout

.. function:: get_language_from_request(request, check_path=False)

    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

    :setting:`LANGUAGES` setting.

.. function:: get_supported_language_variant(lang_code, strict=False)

    Returns ``lang_code`` if it's in the :setting:`LANGUAGES` setting, possibly

    selecting a more generic variant. For example, ``'es'`` is returned if

    ``lang_code`` is ``'es-ar'`` and ``'es'`` is in :setting:`LANGUAGES` but

    ``'es-ar'`` isn't.

    If ``strict`` is ``False`` (the default), a country-specific variant may

    be returned when neither the language code nor its generic variant is found.

    For example, if only ``'es-co'`` is in :setting:`LANGUAGES`, that's

    returned for ``lang_code``\s like ``'es'`` and ``'es-ar'``. Those matches

    aren't returned if ``strict=True``.

    Raises :exc:`LookupError` if nothing is found.

.. function:: to_locale(language)

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

.. function:: templatize(src)

    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.