6 Jinja2 supports extensions that can add extra filters, tests, globals or even
7 extend the parser. The main motivation of extensions is it to move often used
8 code into a reusable class like adding support for internationalization.
14 Extensions are added to the Jinja2 environment at creation time. Once the
15 environment is created additional extensions cannot be added. To add an
16 extension pass a list of extension classes or import paths to the
17 `environment` parameter of the :class:`Environment` constructor. The following
18 example creates a Jinja2 environment with the i18n extension loaded::
20 jinja_env = Environment(extensions=['jinja2.ext.i18n'])
28 Jinja2 currently comes with one extension, the i18n extension. It can be
29 used in combination with `gettext`_ or `babel`_. If the i18n extension is
30 enabled Jinja2 provides a `trans` statement that marks the wrapped string as
31 translatable and calls `gettext`.
33 After enabling dummy `_` function that forwards calls to `gettext` is added
34 to the environment globals. An internationalized application then has to
35 provide at least an `gettext` and optoinally a `ngettext` function into the
36 namespace. Either globally or for each rendering.
38 After enabling of the extension the environment provides the following
41 .. method:: jinja2.Environment.install_gettext_translations(translations)
43 Installs a translation globally for that environment. The tranlations
44 object provided must implement at least `ugettext` and `ungettext`.
45 The `gettext.NullTranslations` and `gettext.GNUTranslations` classes
46 as well as `Babel`_\s `Translations` class are supported.
48 .. method:: jinja2.Environment.install_null_translations()
50 Install dummy gettext functions. This is useful if you want to prepare
51 the application for internationalization but don't want to implement the
52 full internationalization system yet.
54 .. method:: jinja2.Environment.uninstall_gettext_translations()
56 Uninstall the translations again.
58 .. method:: jinja2.Environment.extract_translations(source)
60 Extract localizable strings from the given template node or source.
62 For every string found this function yields a ``(lineno, function,
63 message)`` tuple, where:
65 * `lineno` is the number of the line on which the string was found,
66 * `function` is the name of the `gettext` function used (if the
67 string was extracted from embedded Python code), and
68 * `message` is the string itself (a `unicode` object, or a tuple
69 of `unicode` objects for functions with multiple string arguments).
71 If `Babel`_ is installed :ref:`the babel integration <babel-integration>`
72 can be used to extract strings for babel.
74 For a web application that is available in multiple languages but gives all
75 the users the same language (for example a multilingual forum software
76 installed for a French community) may load the translations once and add the
77 translation methods to the environment at environment generation time::
79 translations = get_gettext_translations()
80 env = Environment(extensions=['jinja.ext.i18n'])
81 env.install_gettext_translations(translations)
83 The `get_gettext_translations` function would return the translator for the
84 current configuration. (For example by using `gettext.find`)
86 The usage of the `i18n` extension for template designers is covered as part
87 :ref:`of the template documentation <i18n-in-templates>`.
89 .. _gettext: http://docs.python.org/dev/library/gettext
90 .. _Babel: http://babel.edgewall.org/
93 .. _writing-extensions:
98 .. module:: jinja2.ext
100 By writing extensions you can add custom tags to Jinja2. This is a non trival
101 task and usually not needed as the default tags and expressions cover all
102 common use cases. The i18n extension is a good example of why extensions are
103 useful, another one would be fragment caching.
105 When writing extensions you have to keep in mind that you are working with the
106 Jinja2 template compiler which does not validate the node tree you are possing
107 to it. If the AST is malformed you will get all kinds of compiler or runtime
108 errors that are horrible to debug. Always make sure you are using the nodes
109 you create correctly. The API documentation below shows which nodes exist and
115 The following example implements a `cache` tag for Jinja2 by using the
116 `Werkzeug`_ caching contrib module:
118 .. literalinclude:: cache_extension.py
121 And here is how you use it in an environment::
123 from jinja2 import Environment
124 from werkzeug.contrib.cache import SimpleCache
126 env = Environment(extensions=[FragmentCacheExtension])
127 env.fragment_cache = SimpleCache()
129 .. _Werkzeug: http://werkzeug.pocoo.org/
134 Extensions always have to extend the :class:`jinja2.ext.Extension` class:
136 .. autoclass:: Extension
137 :members: parse, attr, call_method
139 .. attribute:: identifier
141 The identifier of the extension. This is always the true import name
142 of the extension class and must not be changed.
146 If the extension implements custom tags this is a set of tag names
147 the extension is listening for.
152 The parser passed to :meth:`Extension.parse` provides ways to parse
153 expressions of different types. The following methods may be used by
156 .. autoclass:: jinja2.parser.Parser
157 :members: parse_expression, parse_tuple, parse_assign_target,
158 parse_statements, skip_colon, skip_comma, free_identifier
160 .. attribute:: filename
162 The filename of the template the parser processes. This is **not**
163 the load name of the template which is unavailable at parsing time.
164 For templates that were not loaded form the file system this is
167 .. attribute:: stream
169 The current :class:`~jinja2.lexer.TokenStream`
171 .. autoclass:: jinja2.lexer.TokenStream
172 :members: push, look, eos, skip, next, expect
174 .. attribute:: current
176 The current :class:`~jinja2.lexer.Token`.
178 .. autoclass:: jinja2.lexer.Token
179 :members: test, test_any
181 .. attribute:: lineno
183 The line number of the token
187 The type of the token. This string is interned so you may compare
188 it with arbitrary strings using the `is` operator.
192 The value of the token.
197 The AST (Abstract Syntax Tree) is used to represent a template after parsing.
198 It's build of nodes that the compiler then converts into executable Python
199 code objects. Extensions that provide custom statements can return nodes to
200 execute custom Python code.
202 The list below describes all nodes that are currently available. The AST may
203 change between Jinja2 versions but will stay backwards compatible.
205 For more information have a look at the repr of :meth:`jinja2.Environment.parse`.
207 .. module:: jinja2.nodes
211 .. autoexception:: Impossible