# Django 2.1.8.dev20190330215650 documentation

# 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.

## `django.utils.cache`

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

`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.

`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).

`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 `CACHE_MIDDLEWARE_SECONDS` setting is used by default.

`add_never_cache_headers`(response)

  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)

  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)

  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)

  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 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.

## `django.utils.dateparse`

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 `datetime` module.
- 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.

`parse_date`(value)

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

`parse_time`(value)

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

  UTC offsets aren't supported; if `value` describes one, the result is `None`.

`parse_datetime`(value)

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

  UTC offsets are supported; if `value` describes one, the result's `tzinfo` attribute is a `FixedOffset` instance.

`parse_duration`(value)

  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.

## `django.utils.decorators`

`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 decorating class based views for example usage.

`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()`).

`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 `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

## `django.utils.encoding`

`python_2_unicode_compatible`()

  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')

  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.

`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_text(strings_only=True)`.

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

  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 objects.

`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.

`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.

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

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

  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).

`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.

`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.

`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 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.

`escape_uri_path`(path)

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

## `django.utils.feedgenerator`

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 Weblog 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

`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().

  `__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.

  `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.

  `num_items`()
  `root_attributes`()

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

  `add_root_elements`(handler)

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

  `item_attributes`(item)

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

  `add_item_elements`(handler, item)

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

  `write`(outfile, encoding)

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

  `writeString`(encoding)

    Returns the feed in the given encoding as a string.

  `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: https://tools.ietf.org/html/rfc4287

## `django.utils.functional`

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:

      {% 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"]

  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 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 write:

      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 above:

      x = person.friends         # calls first time
      y = person.get_friends()   # calls again
      z = person.friends         # does not call
      x is z                     # is True

  경고

  `cached_property` doesn't work properly with a mangled name unless it's passed a `name` of the form `_Class__attribute`:

      __friends = cached_property(get_friends, name='_Person__friends')

`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 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.

`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, simply 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`

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.

`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 `mark_safe()` applied.

`conditional_escape`(text)

  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)

  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" % (
          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 `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)

  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 `conditional_escape()`.

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

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

`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 `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 Python library.

`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 `mark_safe()`. Ensure the `__str__()` method does indeed return text that doesn't require HTML escaping.

## `django.utils.http`

`urlencode`(query, doseq=False)

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

`cookie_date`(epoch_seconds=None)

  버전 2.1 폐지: Use `http_date()` instead, which follows the latest RFC.

  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`.

`http_date`(epoch_seconds=None)

  Formats the time to match the RFC 1123 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`.

`base36_to_int`(s)

  Converts a base 36 string to an integer.

`int_to_base36`(i)

  Converts a positive integer to a base 36 string.

`urlsafe_base64_encode`(s)

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

`urlsafe_base64_decode`(s)

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

## `django.utils.module_loading`

Functions for working with Python modules.

`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`

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 `SafeText`.

class `SafeText`

  A `str` subclass that has been specifically marked as "safe" for HTML output purposes.

`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 `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'>

## `django.utils.text`

`format_lazy`(format_string, *args, **kwargs)

  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')),
               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/`.

`slugify`(value, allow_unicode=False)

  Converts a string to a URL slug by:

  1. Converting to ASCII if `allow_unicode` is `False` (the default).
  2. Removing characters that aren't alphanumerics, underscores, hyphens, or whitespace.
  3. Removing leading and trailing whitespace.
  4. Converting to lowercase.
  5. Replacing any whitespace or repeated dashes with single dashes.

  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'

## `django.utils.timezone`

`utc`

  `tzinfo` instance that represents UTC.

class `FixedOffset`(offset=None, name=None)

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

`get_fixed_timezone`(offset)

  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.

`get_default_timezone`()

  Returns a `tzinfo` instance that represents the default time zone.

`get_default_timezone_name`()

  Returns the name of the default time zone.

`get_current_timezone`()

  Returns a `tzinfo` instance that represents the current time zone.

`get_current_timezone_name`()

  Returns the name of the current time zone.

`activate`(timezone)

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

`deactivate`()

  Unsets the current time zone.

`override`(timezone)

  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)

  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()` instead.

`localdate`(value=None, timezone=None)

  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.

`now`()

  Returns a `datetime` that represents the current point in time. Exactly what's returned depends on the value of `USE_TZ`:

  - 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.

`is_aware`(value)

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

`is_naive`(value)

  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)

  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)

  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.

## `django.utils.translation`

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`.

`gettext`(message)

`ugettext`(message)

  Translates `message` and returns it as a string.

`pgettext`(context, message)

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

  For more information, see Contextual markers.

`gettext_lazy`(message)

`ugettext_lazy`(message)

`pgettext_lazy`(context, message)

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

  See lazy translations documentation.

`gettext_noop`(message)

`ugettext_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.

`ngettext`(singular, plural, number)

`ungettext`(singular, plural, number)

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

`npgettext`(context, singular, plural, number)

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

`ngettext_lazy`(singular, plural, number)

`ungettext_lazy`(singular, plural, number)

`npgettext_lazy`(context, singular, plural, number)

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

  See lazy translations documentation.

`activate`(language)

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

`deactivate`()

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

`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.

`override`(language, deactivate=False)

  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.

`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.

`get_language`()

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

`get_language_bidi`()

  Returns selected language's BiDi layout:

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

`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 `LANGUAGES` setting.

`get_supported_language_variant`(lang_code, strict=False)
  New in Django 2.1:

  Returns `lang_code` if it's in the `LANGUAGES` setting, possibly selecting a more generic variant. For example, `'es'` is returned if `lang_code` is `'es-ar'` and `'es'` is in `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 `LANGUAGES`, that's returned for `lang_code`s like `'es'` and `'es-ar'`. Those matches aren't returned if `strict=True`.

  Raises `LookupError` if nothing is found.

`to_locale`(language)

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

`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.

`LANGUAGE_SESSION_KEY`

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