django/docs/ref/utils.txt

============
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 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 2616 section 14.44`_.

.. _RFC 2616 section 14.44: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.44

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:

 * ``ETag``
 * ``Last-Modified``
 * ``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.

.. function:: add_never_cache_headers(response)

Adds headers to a response to indicate that a page should never be cached.

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

.. function:: 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``.

.. function:: 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.

SortedDict
==========

.. module:: django.utils.datastructures
   :synopsis: A dictionary that keeps its keys in the order in which they're inserted.

.. class:: django.utils.datastructures.SortedDict

Methods
-------

Extra methods that ``SortedDict`` adds to the standard Python ``dict`` class.

.. method:: insert(index, key, value)

Inserts the key, value pair before the item with the given index.

.. method:: value_for_index(index)

Returns the value of the item at the given zero-based index.

Creating new SortedDict
-----------------------

Creating a new ``SortedDict`` must be done in a way where ordering is
guaranteed. For example::

    SortedDict({'b': 1, 'a': 2, 'c': 3})

will not work. Passing in a basic Python ``dict`` could produce unreliable
results. Instead do::

    SortedDict([('b', 1), ('a', 2), ('c', 3)])

``django.utils.encoding``
=========================

.. module:: django.utils.encoding
   :synopsis: A series of helper classes and function to manage character encoding.

.. class:: StrAndUnicode

A class whose ``__str__`` returns its ``__unicode__`` as a UTF-8 bytestring.
Useful as a mix-in.

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

Returns a ``unicode`` object representing ``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_unicode(strings_only=True)``.

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

Similar to ``smart_unicode``, 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_str(s, encoding='utf-8', strings_only=False, errors='strict')

Returns a bytestring version of ``s``, encoded as specified in ``encoding``.

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`_.  However, since we are
assuming input is either UTF-8 or unicode already, we can simplify things a
little from the full method.

.. _RFC 3987: http://www.ietf.org/rfc/rfc3987.txt

Returns an ASCII string containing the encoded result.

``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=u"Poynter E-Media Tidbits",
    ...     link=u"http://www.poynter.org/column.asp?id=31",
    ...     description=u"A group weblog by the sharpest minds in online media/journalism/publishing.",
    ...     language=u"en",
    ... )
    >>> feed.add_item(
    ...     title="Hello",
    ...     link=u"http://www.holovaty.com/test/",
    ...     description="Testing."
    ... )
    >>> fp = open('test.rss', 'w')
    >>> feed.write(fp, 'utf-8')
    >>> fp.close()

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

For definitions of the different versions of RSS, see:
http://diveintomark.org/archives/2004/02/04/incompatible-rss

.. function:: get_tag_uri(url, date)

Creates a TagURI.

See http://diveintomark.org/archives/2004/05/28/howto-atom-id

SyndicationFeed
---------------

.. class:: SyndicationFeed

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

Methods
~~~~~~~

.. method:: add_item(title, link, description, [author_email=None, author_name=None, author_link=None, pubdate=None, comments=None, unique_id=None, enclosure=None, categories=(), item_copyright=None, ttl=None, **kwargs])

Adds an item to the feed. All args are expected to be Python ``unicode``
objects except ``pubdate``, which is a ``datetime.datetime`` object, and
``enclosure``, which is an instance of the ``Enclosure`` class.

.. 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 item's ``pubdate``. If none of them have a ``pubdate``,
this returns the current date/time.

Enclosure
---------

.. class:: Enclosure

Represents an RSS enclosure

RssFeed
-------

.. class:: RssFeed(SyndicationFeed)

Rss201rev2Feed
--------------

.. class:: Rss201rev2Feed(RssFeed)

Spec: http://blogs.law.harvard.edu/tech/rss

Atom1Feed
---------

.. class:: Atom1Feed(SyndicationFeed)

Spec: http://atompub.org/2005/07/11/draft-ietf-atompub-format-10.html

``django.utils.http``
=====================

.. module:: django.utils.http
   :synopsis: HTTP helper functions. (URL encoding, cookie handling, ...)

.. function:: urlquote(url, safe='/')

A version of Python's ``urllib.quote()`` function that can operate on unicode
strings. The url is first UTF-8 encoded before quoting. The returned string
can safely be used as part of an argument to a subsequent ``iri_to_uri()``
call without double-quoting occurring. Employs lazy execution.

.. function:: urlquote_plus(url, safe='')

A version of Python's urllib.quote_plus() function that can operate on unicode
strings. The url is first UTF-8 encoded before quoting. The returned string can
safely be used as part of an argument to a subsequent iri_to_uri() call without
double-quoting occurring. Employs lazy execution.

.. function:: urlencode(query, doseq=0)

A version of Python's urllib.urlencode() function that can operate on unicode
strings. The parameters are first case to UTF-8 encoded strings and then
encoded as per normal.

.. function:: cookie_date(epoch_seconds=None)

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``.

.. function:: http_date(epoch_seconds=None)

Formats the time to match the RFC 1123 date format as specified by HTTP
`RFC 2616`_ section 3.3.1.

.. _RFC 2616: http://www.w3.org/Protocols/rfc2616/rfc2616.txt

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)

Converted a base 36 string to an integer

.. function:: int_to_base36(i)

Converts an integer to a base36 string

``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 string subclass that has been specifically marked as "safe" (requires no
further escaping) for HTML output purposes.

.. class:: SafeUnicode

A unicode subclass that has been specifically marked as "safe" 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 or unicode object is appropriate.

Can be called multiple times on a single string.

.. function:: mark_for_escaping(s)

Explicitly mark a string as requiring HTML escaping upon output. Has no effect
on ``SafeData`` subclasses.

Can be called multiple times on a single string (the resulting escaping is only
applied once).

``django.utils.translation``
============================

.. module:: django.utils.translation
   :synopsis: Internationalization support.

For a complete discussion on the usage of the following see the
:doc:`Internationalization documentation </topics/i18n/internationalization>`.

.. function:: gettext(message)

Translates ``message`` and returns it in a UTF-8 bytestring

.. function:: ugettext(message)

Translates ``message`` and returns it in a unicode string

.. function:: gettext_lazy(message)
.. function:: ugettext_lazy(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`` in a UTF-8 bytestring

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

Translates ``singular`` and ``plural`` and returns the appropriate string based
on ``number`` in a unicode string

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

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

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

.. function:: string_concat(*strings)

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

.. function:: activate(language)

Fetches the translation object for a given tuple of application name and
language and installs it as the current translation object for the current
thread.

.. function:: deactivate()

De-installs 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:: get_language()

Returns the currently selected language code.

.. function:: get_language_bidi()

Returns selected language's BiDi layout:

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

.. function:: get_date_formats()

Checks whether translation files provide a translation for some technical
message ID to store date and time formats. If it doesn't contain one, the
formats provided in the settings will be used.

.. function:: get_language_from_request(request)

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.

.. 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.

``django.utils.tzinfo``
=======================

.. module:: django.utils.tzinfo
   :synopsis: Implementation of ``tzinfo`` classes for use with ``datetime.datetime``.

.. class:: FixedOffset

Fixed offset in minutes east from UTC.

.. class:: LocalTimezone

Proxy timezone information from time module.