Django 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 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.

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(responsecache_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.

add_never_cache_headers(response)

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

patch_vary_headers(responsenewheaders)

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(requestkey_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(requestresponsecache_timeout=Nonekey_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

class django.utils.datastructures.SortedDict

Methods

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

insert(indexkeyvalue)

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

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

class StrAndUnicode

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

smart_unicode(sencoding='utf-8'strings_only=Falseerrors='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.

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).

force_unicode(sencoding='utf-8'strings_only=Falseerrors='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.

smart_str(sencoding='utf-8'strings_only=Falseerrors='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.

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.

Returns an ASCII string containing the encoded result.

django.utils.feedgenerator

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

get_tag_uri(urldate)

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().

__init__(titlelinkdescription[language=Noneauthor_email=Noneauthor_name=Noneauthor_link=Nonesubtitle=Nonecategories=Nonefeed_url=Nonefeed_copyright=Nonefeed_guid=Nonettl=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 Unicode objects, except categories, which should be a sequence of Unicode objects.

add_item(titlelinkdescription[author_email=Noneauthor_name=Noneauthor_link=Nonepubdate=Nonecomments=Noneunique_id=Noneenclosure=Nonecategories=()item_copyright=Nonettl=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.

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(handleritem)

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

write(outfileencoding)

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 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

RssUserland091Feed

class RssUserland091Feed(RssFeed)

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

Atom1Feed

class Atom1Feed(SyndicationFeed)

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

django.utils.http

urlquote(urlsafe='/')

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.

urlquote_plus(urlsafe='')

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.

urlencode(querydoseq=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.

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.

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.

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)

Converted a base 36 string to an integer

int_to_base36(i)

Converts an integer to a base36 string

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 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.

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.

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

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

gettext(message)

Translates message and returns it in a UTF-8 bytestring

ugettext(message)

Translates message and returns it in a unicode string

gettext_lazy(message)
ugettext_lazy(message)

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

See lazy translations documentation.

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.

ngettext(singularpluralnumber)

Translates singular and plural and returns the appropriate string based on number in a UTF-8 bytestring

ungettext(singularpluralnumber)

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

ngettext_lazy(singularpluralnumber)
ungettext_lazy(singularpluralnumber)

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

See lazy translations documentation.

string_concat(*strings)

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

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.

deactivate()

De-installs 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.

get_language()

Returns the currently selected language code.

get_language_bidi()

Returns selected language's BiDi layout:

  • False = left-to-right layout
  • True = right-to-left layout
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.

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.

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.

django.utils.tzinfo

class FixedOffset

Fixed offset in minutes east from UTC.

class LocalTimezone

Proxy timezone information from time module.

Questions/Feedback

Having trouble? We'd like to help!

This document is for an insecure version of Django that is no longer supported. Please upgrade to a newer release!