5 :synopsis: public Jinja2 API
7 This document describes the API to Jinja2 and not the template language. It
8 will be most useful as reference to those implementing the template interface
9 to the application and not those who are creating Jinja2 templates.
14 Jinja2 uses a central object called the template :class:`Environment`.
15 Instances of this class are used to store the configuration, global objects
16 and are used to load templates from the file system or other locations.
17 Even if you are creating templates from strings by using the constructor of
18 :class:`Template` class, an environment is created automatically for you,
21 Most applications will create one :class:`Environment` object on application
22 initialization and use that to load templates. In some cases it's however
23 useful to have multiple environments side by side, if different configurations
26 The simplest way to configure Jinja2 to load templates for your application
27 looks roughly like this::
29 from jinja2 import Environment, PackageLoader
30 env = Environment(loader=PackageLoader('yourapplication', 'templates'))
32 This will create a template environment with the default settings and a
33 loader that looks up the templates in the `templates` folder inside the
34 `yourapplication` python package. Different loaders are available
35 and you can also write your own if you want to load templates from a
36 database or other resources.
38 To load a template from this environment you just have to call the
39 :meth:`get_template` method which then returns the loaded :class:`Template`::
41 template = env.get_template('mytemplate.html')
43 To render it with some variables, just call the :meth:`render` method::
45 print template.render(the='variables', go='here')
47 Using a template loader rather then passing strings to :class:`Template`
48 or :meth:`Environment.from_string` has multiple advantages. Besides being
49 a lot easier to use it also enables template inheritance.
55 Jinja2 is using Unicode internally which means that you have to pass Unicode
56 objects to the render function or bytestrings that only consist of ASCII
57 characters. Additionally newlines are normalized to one end of line
58 sequence which is per default UNIX style (``\n``).
60 Python 2.x supports two ways of representing string objects. One is the
61 `str` type and the other is the `unicode` type, both of which extend a type
62 called `basestring`. Unfortunately the default is `str` which should not
63 be used to store text based information unless only ASCII characters are
64 used. With Python 2.6 it is possible to make `unicode` the default on a per
65 module level and with Python 3 it will be the default.
67 To explicitly use a Unicode string you have to prefix the string literal
68 with a `u`: ``u'Hänsel und Gretel sagen Hallo'``. That way Python will
69 store the string as Unicode by decoding the string with the character
70 encoding from the current Python module. If no encoding is specified this
71 defaults to 'ASCII' which means that you can't use any non ASCII identifier.
73 To set a better module encoding add the following comment to the first or
74 second line of the Python module using the Unicode literal::
76 # -*- coding: utf-8 -*-
78 We recommend utf-8 as Encoding for Python modules and templates as it's
79 possible to represent every Unicode character in utf-8 and because it's
80 backwards compatible to ASCII. For Jinja2 the default encoding of templates
81 is assumed to be utf-8.
83 It is not possible to use Jinja2 to process non-Unicode data. The reason
84 for this is that Jinja2 uses Unicode already on the language level. For
85 example Jinja2 treats the non-breaking space as valid whitespace inside
86 expressions which requires knowledge of the encoding or operating on an
89 For more details about Unicode in Python have a look at the excellent
90 `Unicode documentation`_.
92 Another important thing is how Jinja2 is handling string literals in
93 templates. A naive implementation would be using Unicode strings for
94 all string literals but it turned out in the past that this is problematic
95 as some libraries are typechecking against `str` explicitly. For example
96 `datetime.strftime` does not accept Unicode arguments. To not break it
97 completely Jinja2 is returning `str` for strings that fit into ASCII and
98 for everything else `unicode`:
100 >>> m = Template(u"{% set a, b = 'foo', 'föö' %}").module
107 .. _Unicode documentation: http://docs.python.org/dev/howto/unicode.html
112 The high-level API is the API you will use in the application to load and
113 render Jinja2 templates. The :ref:`low-level-api` on the other side is only
114 useful if you want to dig deeper into Jinja2 or :ref:`develop extensions
117 .. autoclass:: Environment([options])
118 :members: from_string, get_template, select_template,
119 get_or_select_template, join_path, extend, compile_expression
121 .. attribute:: shared
123 If a template was created by using the :class:`Template` constructor
124 an environment is created automatically. These environments are
125 created as shared environments which means that multiple templates
126 may have the same anonymous environment. For all shared environments
127 this attribute is `True`, else `False`.
129 .. attribute:: sandboxed
131 If the environment is sandboxed this attribute is `True`. For the
132 sandbox mode have a look at the documentation for the
133 :class:`~jinja2.sandbox.SandboxedEnvironment`.
135 .. attribute:: filters
137 A dict of filters for this environment. As long as no template was
138 loaded it's safe to add new filters or remove old. For custom filters
139 see :ref:`writing-filters`. For valid filter names have a look at
140 :ref:`identifier-naming`.
144 A dict of test functions for this environment. As long as no
145 template was loaded it's safe to modify this dict. For custom tests
146 see :ref:`writing-tests`. For valid test names have a look at
147 :ref:`identifier-naming`.
149 .. attribute:: globals
151 A dict of global variables. These variables are always available
152 in a template. As long as no template was loaded it's safe
153 to modify this dict. For more details see :ref:`global-namespace`.
154 For valid object names have a look at :ref:`identifier-naming`.
156 .. automethod:: overlay([options])
158 .. method:: undefined([hint, obj, name, exc])
160 Creates a new :class:`Undefined` object for `name`. This is useful
161 for filters or functions that may return undefined objects for
162 some operations. All parameters except of `hint` should be provided
163 as keyword parameters for better readability. The `hint` is used as
164 error message for the exception if provided, otherwise the error
165 message will be generated from `obj` and `name` automatically. The exception
166 provided as `exc` is raised if something with the generated undefined
167 object is done that the undefined object does not allow. The default
168 exception is :exc:`UndefinedError`. If a `hint` is provided the
169 `name` may be ommited.
171 The most common way to create an undefined object is by providing
174 return environment.undefined(name='some_name')
176 This means that the name `some_name` is not defined. If the name
177 was from an attribute of an object it makes sense to tell the
178 undefined object the holder object to improve the error message::
180 if not hasattr(obj, 'attr'):
181 return environment.undefined(obj=obj, name='attr')
183 For a more complex example you can provide a hint. For example
184 the :func:`first` filter creates an undefined object that way::
186 return environment.undefined('no first item, sequence was empty')
188 If it the `name` or `obj` is known (for example because an attribute
189 was accessed) it shold be passed to the undefined object, even if
190 a custom `hint` is provided. This gives undefined objects the
191 possibility to enhance the error message.
193 .. autoclass:: Template
194 :members: module, make_module
196 .. attribute:: globals
198 The dict with the globals of that template. It's unsafe to modify
199 this dict as it may be shared with other templates or the environment
200 that loaded the template.
204 The loading name of the template. If the template was loaded from a
205 string this is `None`.
207 .. attribute:: filename
209 The filename of the template on the file system if it was loaded from
210 there. Otherwise this is `None`.
212 .. automethod:: render([context])
214 .. automethod:: generate([context])
216 .. automethod:: stream([context])
219 .. autoclass:: jinja2.environment.TemplateStream()
220 :members: disable_buffering, enable_buffering, dump
223 .. _identifier-naming:
228 Jinja2 uses the regular Python 2.x naming rules. Valid identifiers have to
229 match ``[a-zA-Z_][a-zA-Z0-9_]*``. As a matter of fact non ASCII characters
230 are currently not allowed. This limitation will probably go away as soon as
231 unicode identifiers are fully specified for Python 3.
233 Filters and tests are looked up in separate namespaces and have slightly
234 modified identifier syntax. Filters and tests may contain dots to group
235 filters and tests by topic. For example it's perfectly valid to add a
236 function into the filter dict and call it `to.unicode`. The regular
237 expression for filter and test identifiers is
238 ``[a-zA-Z_][a-zA-Z0-9_]*(\.[a-zA-Z_][a-zA-Z0-9_]*)*```.
244 These classes can be used as undefined types. The :class:`Environment`
245 constructor takes an `undefined` parameter that can be one of those classes
246 or a custom subclass of :class:`Undefined`. Whenever the template engine is
247 unable to look up a name or access an attribute one of those objects is
248 created and returned. Some operations on undefined values are then allowed,
251 The closest to regular Python behavior is the `StrictUndefined` which
252 disallows all operations beside testing if it's an undefined object.
254 .. autoclass:: jinja2.Undefined()
256 .. attribute:: _undefined_hint
258 Either `None` or an unicode string with the error message for
259 the undefined object.
261 .. attribute:: _undefined_obj
263 Either `None` or the owner object that caused the undefined object
264 to be created (for example because an attribute does not exist).
266 .. attribute:: _undefined_name
268 The name for the undefined variable / attribute or just `None`
269 if no such information exists.
271 .. attribute:: _undefined_exception
273 The exception that the undefined object wants to raise. This
274 is usually one of :exc:`UndefinedError` or :exc:`SecurityError`.
276 .. method:: _fail_with_undefined_error(\*args, \**kwargs)
278 When called with any arguments this method raises
279 :attr:`_undefined_exception` with an error message generated
280 from the undefined hints stored on the undefined object.
282 .. autoclass:: jinja2.DebugUndefined()
284 .. autoclass:: jinja2.StrictUndefined()
286 Undefined objects are created by calling :attr:`undefined`.
288 .. admonition:: Implementation
290 :class:`Undefined` objects are implemented by overriding the special
291 `__underscore__` methods. For example the default :class:`Undefined`
292 class implements `__unicode__` in a way that it returns an empty
293 string, however `__int__` and others still fail with an exception. To
294 allow conversion to int by returning ``0`` you can implement your own::
296 class NullUndefined(Undefined):
302 To disallow a method, just override it and raise
303 :attr:`~Undefined._undefined_exception`. Because this is a very common
304 idom in undefined objects there is the helper method
305 :meth:`~Undefined._fail_with_undefined_error` that does the error raising
306 automatically. Here a class that works like the regular :class:`Undefined`
307 but chokes on iteration::
309 class NonIterableUndefined(Undefined):
310 __iter__ = Undefined._fail_with_undefined_error
316 .. autoclass:: jinja2.runtime.Context()
317 :members: resolve, get_exported, get_all
319 .. attribute:: parent
321 A dict of read only, global variables the template looks up. These
322 can either come from another :class:`Context`, from the
323 :attr:`Environment.globals` or :attr:`Template.globals` or points
324 to a dict created by combining the globals with the variables
325 passed to the render function. It must not be altered.
329 The template local variables. This list contains environment and
330 context functions from the :attr:`parent` scope as well as local
331 modifications and exported variables from the template. The template
332 will modify this dict during template evaluation but filters and
333 context functions are not allowed to modify it.
335 .. attribute:: environment
337 The environment that loaded the template.
339 .. attribute:: exported_vars
341 This set contains all the names the template exports. The values for
342 the names are in the :attr:`vars` dict. In order to get a copy of the
343 exported variables as dict, :meth:`get_exported` can be used.
347 The load name of the template owning this context.
349 .. attribute:: blocks
351 A dict with the current mapping of blocks in the template. The keys
352 in this dict are the names of the blocks, and the values a list of
353 blocks registered. The last item in each list is the current active
354 block (latest in the inheritance chain).
356 .. automethod:: jinja2.runtime.Context.call(callable, \*args, \**kwargs)
359 .. admonition:: Implementation
361 Context is immutable for the same reason Python's frame locals are
362 immutable inside functions. Both Jinja2 and Python are not using the
363 context / frame locals as data storage for variables but only as primary
366 When a template accesses a variable the template does not define, Jinja2
367 looks up the variable in the context, after that the variable is treated
368 as if it was defined in the template.
376 Loaders are responsible for loading templates from a resource such as the
377 file system. The environment will keep the compiled modules in memory like
378 Python's `sys.modules`. Unlike `sys.modules` however this cache is limited in
379 size by default and templates are automatically reloaded.
380 All loaders are subclasses of :class:`BaseLoader`. If you want to create your
381 own loader, subclass :class:`BaseLoader` and override `get_source`.
383 .. autoclass:: jinja2.BaseLoader
384 :members: get_source, load
386 Here a list of the builtin loaders Jinja2 provides:
388 .. autoclass:: jinja2.FileSystemLoader
390 .. autoclass:: jinja2.PackageLoader
392 .. autoclass:: jinja2.DictLoader
394 .. autoclass:: jinja2.FunctionLoader
396 .. autoclass:: jinja2.PrefixLoader
398 .. autoclass:: jinja2.ChoiceLoader
406 Jinja 2.1 and higher support external bytecode caching. Bytecode caches make
407 it possible to store the generated bytecode on the file system or a different
408 location to avoid parsing the templates on first use.
410 This is especially useful if you have a web application that is initialized on
411 the first request and Jinja compiles many templates at once which slows down
414 To use a bytecode cache, instanciate it and pass it to the :class:`Environment`.
416 .. autoclass:: jinja2.BytecodeCache
417 :members: load_bytecode, dump_bytecode, clear
419 .. autoclass:: jinja2.bccache.Bucket
420 :members: write_bytecode, load_bytecode, bytecode_from_string,
421 bytecode_to_string, reset
423 .. attribute:: environment
425 The :class:`Environment` that created the bucket.
429 The unique cache key for this bucket
433 The bytecode if it's loaded, otherwise `None`.
436 Builtin bytecode caches:
438 .. autoclass:: jinja2.FileSystemBytecodeCache
440 .. autoclass:: jinja2.MemcachedBytecodeCache
446 These helper functions and classes are useful if you add custom filters or
447 functions to a Jinja2 environment.
449 .. autofunction:: jinja2.environmentfilter
451 .. autofunction:: jinja2.contextfilter
453 .. autofunction:: jinja2.environmentfunction
455 .. autofunction:: jinja2.contextfunction
457 .. function:: escape(s)
459 Convert the characters ``&``, ``<``, ``>``, ``'``, and ``"`` in string `s`
460 to HTML-safe sequences. Use this if you need to display text that might
461 contain such characters in HTML. This function will not escaped objects
462 that do have an HTML representation such as already escaped data.
464 The return value is a :class:`Markup` string.
466 .. autofunction:: jinja2.clear_caches
468 .. autofunction:: jinja2.is_undefined
470 .. autoclass:: jinja2.Markup([string])
471 :members: escape, unescape, striptags
475 The Jinja2 :class:`Markup` class is compatible with at least Pylons and
476 Genshi. It's expected that more template engines and framework will pick
477 up the `__html__` concept soon.
483 .. autoexception:: jinja2.TemplateError
485 .. autoexception:: jinja2.UndefinedError
487 .. autoexception:: jinja2.TemplateNotFound
489 .. autoexception:: jinja2.TemplatesNotFound
491 .. autoexception:: jinja2.TemplateSyntaxError
493 .. attribute:: message
495 The error message as utf-8 bytestring.
497 .. attribute:: lineno
499 The line number where the error occurred
503 The load name for the template as unicode string.
505 .. attribute:: filename
507 The filename that loaded the template as bytestring in the encoding
508 of the file system (most likely utf-8 or mbcs on Windows systems).
510 The reason why the filename and error message are bytestrings and not
511 unicode strings is that Python 2.x is not using unicode for exceptions
512 and tracebacks as well as the compiler. This will change with Python 3.
514 .. autoexception:: jinja2.TemplateAssertionError
522 Custom filters are just regular Python functions that take the left side of
523 the filter as first argument and the the arguments passed to the filter as
524 extra arguments or keyword arguments.
526 For example in the filter ``{{ 42|myfilter(23) }}`` the function would be
527 called with ``myfilter(42, 23)``. Here for example a simple filter that can
528 be applied to datetime objects to format them::
530 def datetimeformat(value, format='%H:%M / %d-%m-%Y'):
531 return value.strftime(format)
533 You can register it on the template environment by updating the
534 :attr:`~Environment.filters` dict on the environment::
536 environment.filters['datetimeformat'] = datetimeformat
538 Inside the template it can then be used as follows:
540 .. sourcecode:: jinja
542 written on: {{ article.pub_date|datetimeformat }}
543 publication date: {{ article.pub_date|datetimeformat('%d-%m-%Y') }}
545 Filters can also be passed the current template context or environment. This
546 is useful if a filter wants to return an undefined value or check the current
547 :attr:`~Environment.autoescape` setting. For this purpose two decorators
548 exist: :func:`environmentfilter` and :func:`contextfilter`.
550 Here a small example filter that breaks a text into HTML line breaks and
551 paragraphs and marks the return value as safe HTML string if autoescaping is
555 from jinja2 import environmentfilter, Markup, escape
557 _paragraph_re = re.compile(r'(?:\r\n|\r|\n){2,}')
560 def nl2br(environment, value):
561 result = u'\n\n'.join(u'<p>%s</p>' % p.replace('\n', '<br>\n')
562 for p in _paragraph_re.split(escape(value)))
563 if environment.autoescape:
564 result = Markup(result)
567 Context filters work the same just that the first argument is the current
568 active :class:`Context` rather then the environment.
576 Tests work like filters just that there is no way for a test to get access
577 to the environment or context and that they can't be chained. The return
578 value of a test should be `True` or `False`. The purpose of a test is to
579 give the template designers the possibility to perform type and conformability
582 Here a simple test that checks if a variable is a prime number::
589 for i in xrange(2, int(math.ceil(math.sqrt(n))) + 1):
595 You can register it on the template environment by updating the
596 :attr:`~Environment.tests` dict on the environment::
598 environment.tests['prime'] = is_prime
600 A template designer can then use the test like this:
602 .. sourcecode:: jinja
607 42 is not a prime number
611 .. _global-namespace:
616 Variables stored in the :attr:`Environment.globals` dict are special as they
617 are available for imported templates too, even if they are imported without
618 context. This is the place where you can put variables and functions
619 that should be available all the time. Additionally :attr:`Template.globals`
620 exist that are variables available to a specific template that are available
621 to all :meth:`~Template.render` calls.
629 The low level API exposes functionality that can be useful to understand some
630 implementation details, debugging purposes or advanced :ref:`extension
631 <jinja-extensions>` techniques. Unless you know exactly what you are doing we
632 don't recommend using any of those.
634 .. automethod:: Environment.lex
636 .. automethod:: Environment.parse
638 .. automethod:: Environment.preprocess
640 .. automethod:: Template.new_context
642 .. method:: Template.root_render_func(context)
644 This is the low level render function. It's passed a :class:`Context`
645 that has to be created by :meth:`new_context` of the same template or
646 a compatible template. This render function is generated by the
647 compiler from the template code and returns a generator that yields
650 If an exception in the template code happens the template engine will
651 not rewrite the exception but pass through the original one. As a
652 matter of fact this function should only be called from within a
653 :meth:`render` / :meth:`generate` / :meth:`stream` call.
655 .. attribute:: Template.blocks
657 A dict of block render functions. Each of these functions works exactly
658 like the :meth:`root_render_func` with the same limitations.
660 .. attribute:: Template.is_up_to_date
662 This attribute is `False` if there is a newer version of the template
663 available, otherwise `True`.
667 The low-level API is fragile. Future Jinja2 versions will try not to
668 change it in a backwards incompatible way but modifications in the Jinja2
669 core may shine through. For example if Jinja2 introduces a new AST node
670 in later versions that may be returned by :meth:`~Environment.parse`.
675 .. versionadded:: 2.2
677 The meta API returns some information about abstract syntax trees that
678 could help applications to implement more advanced template concepts. All
679 the functions of the meta API operate on an abstract syntax tree as
680 returned by the :meth:`Environment.parse` method.
682 .. autofunction:: jinja2.meta.find_undeclared_variables
684 .. autofunction:: jinja2.meta.find_referenced_templates