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 string 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 my `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`_.
93 .. _Unicode documentation: http://docs.python.org/dev/howto/unicode.html
98 The high-level API is the API you will use in the application to load and
99 render Jinja2 templates. The :ref:`low-level-api` on the other side is only
100 useful if you want to dig deeper into Jinja2 or :ref:`develop extensions
103 .. autoclass:: Environment([options])
104 :members: from_string, get_template, join_path, extend
106 .. attribute:: shared
108 If a template was created by using the :class:`Template` constructor
109 an environment is created automatically. These environments are
110 created as shared environments which means that multiple templates
111 may have the same anonymous environment. For all shared environments
112 this attribute is `True`, else `False`.
114 .. attribute:: sandboxed
116 If the environment is sandboxed this attribute is `True`. For the
117 sandbox mode have a look at the documentation for the
118 :class:`~jinja2.sandbox.SandboxedEnvironment`.
120 .. attribute:: filters
122 A dict of filters for this environment. As long as no template was
123 loaded it's safe to add new filters or remove old. For custom filters
124 see :ref:`writing-filters`. For valid filter names have a look at
125 :ref:`identifier-naming`.
129 A dict of test functions for this environment. As long as no
130 template was loaded it's safe to modify this dict. For custom tests
131 see :ref:`writing-tests`. For valid test names have a look at
132 :ref:`identifier-naming`.
134 .. attribute:: globals
136 A dict of global variables. These variables are always available
137 in a template. As long as no template was loaded it's safe
138 to modify this dict. For more details see :ref:`global-namespace`.
139 For valid object names have a look at :ref:`identifier-naming`.
141 .. automethod:: overlay([options])
143 .. method:: undefined([hint,] [obj,] name[, exc])
145 Creates a new :class:`Undefined` object for `name`. This is useful
146 for filters or functions that may return undefined objects for
147 some operations. All parameters except of `hint` should be provided
148 as keyword parameters for better readability. The `hint` is used as
149 error message for the exception if provided, otherwise the error
150 message generated from `obj` and `name` automatically. The exception
151 provided as `exc` is raised if something with the generated undefined
152 object is done that the undefined object does not allow. The default
153 exception is :exc:`UndefinedError`. If a `hint` is provided the
154 `name` may be ommited.
156 The most common way to create an undefined object is by providing
159 return environment.undefined(name='some_name')
161 This means that the name `some_name` is not defined. If the name
162 was from an attribute of an object it makes sense to tell the
163 undefined object the holder object to improve the error message::
165 if not hasattr(obj, 'attr'):
166 return environment.undefined(obj=obj, name='attr')
168 For a more complex example you can provide a hint. For example
169 the :func:`first` filter creates an undefined object that way::
171 return environment.undefined('no first item, sequence was empty')
173 If it the `name` or `obj` is known (for example because an attribute
174 was accessed) it shold be passed to the undefined object, even if
175 a custom `hint` is provided. This gives undefined objects the
176 possibility to enhance the error message.
178 .. autoclass:: Template
179 :members: module, make_module
181 .. attribute:: globals
183 The dict with the globals of that template. It's unsafe to modify
184 this dict as it may be shared with other templates or the environment
185 that loaded the template.
189 The loading name of the template. If the template was loaded from a
190 string this is `None`.
192 .. attribute:: filename
194 The filename of the template on the file system if it was loaded from
195 there. Otherwise this is `None`.
197 .. automethod:: render([context])
199 .. automethod:: generate([context])
201 .. automethod:: stream([context])
204 .. autoclass:: jinja2.environment.TemplateStream()
205 :members: disable_buffering, enable_buffering
208 .. _identifier-naming:
213 Jinja2 uses the regular Python 2.x naming rules. Valid identifiers have to
214 match ``[a-zA-Z_][a-zA-Z0-9_]*``. As a matter of fact non ASCII characters
215 are currently not allowed. This limitation will probably go away as soon as
216 unicode identifiers are fully specified for Python 3.
218 Filters and tests are looked up in separate namespaces and have slightly
219 modified identifier syntax. Filters and tests may contain dots to group
220 filters and tests by topic. For example it's perfectly valid to add a
221 function into the filter dict and call it `to.unicode`. The regular
222 expression for filter and test identifiers is
223 ``[a-zA-Z_][a-zA-Z0-9_]*(\.[a-zA-Z_][a-zA-Z0-9_]*)*```.
229 These classes can be used as undefined types. The :class:`Environment`
230 constructor takes an `undefined` parameter that can be one of those classes
231 or a custom subclass of :class:`Undefined`. Whenever the template engine is
232 unable to look up a name or access an attribute one of those objects is
233 created and returned. Some operations on undefined values are then allowed,
236 The closest to regular Python behavior is the `StrictUndefined` which
237 disallows all operations beside testing if it's an undefined object.
239 .. autoclass:: jinja2.runtime.Undefined()
241 .. attribute:: _undefined_hint
243 Either `None` or an unicode string with the error message for
244 the undefined object.
246 .. attribute:: _undefined_obj
248 Either `None` or the owner object that caused the undefined object
249 to be created (for example because an attribute does not exist).
251 .. attribute:: _undefined_name
253 The name for the undefined variable / attribute or just `None`
254 if no such information exists.
256 .. attribute:: _undefined_exception
258 The exception that the undefined object wants to raise. This
259 is usually one of :exc:`UndefinedError` or :exc:`SecurityError`.
261 .. method:: _fail_with_undefined_error(\*args, \**kwargs)
263 When called with any arguments this method raises
264 :attr:`_undefined_exception` with an error message generated
265 from the undefined hints stored on the undefined object.
267 .. autoclass:: jinja2.runtime.DebugUndefined()
269 .. autoclass:: jinja2.runtime.StrictUndefined()
271 Undefined objects are created by calling :attr:`undefined`.
273 .. admonition:: Implementation
275 :class:`Undefined` objects are implemented by overriding the special
276 `__underscore__` methods. For example the default :class:`Undefined`
277 class implements `__unicode__` in a way that it returns an empty
278 string, however `__int__` and others still fail with an exception. To
279 allow conversion to int by returning ``0`` you can implement your own::
281 class NullUndefined(Undefined):
287 To disallow a method, just override it and raise
288 :attr:`_undefined_exception`. Because this is a very common idom in
289 undefined objects there is the helper method
290 :meth:`_fail_with_undefined_error`. That does that automatically. Here
291 a class that works like the regular :class:`UndefinedError` but chokes
294 class NonIterableUndefined(Undefined):
295 __iter__ = Undefined._fail_with_undefined_error
301 .. autoclass:: jinja2.runtime.Context()
302 :members: resolve, get_exported, get_all
304 .. attribute:: parent
306 A dict of read only, global variables the template looks up. These
307 can either come from another :class:`Context`, from the
308 :attr:`Environment.globals` or :attr:`Template.globals` or points
309 to a dict created by combining the globals with the variables
310 passed to the render function. It must not be altered.
314 The template local variables. This list contains environment and
315 context functions from the :attr:`parent` scope as well as local
316 modifications and exported variables from the template. The template
317 will modify this dict during template evaluation but filters and
318 context functions are not allowed to modify it.
320 .. attribute:: environment
322 The environment that loaded the template.
324 .. attribute:: exported_vars
326 This set contains all the names the template exports. The values for
327 the names are in the :attr:`vars` dict. In order to get a copy of the
328 exported variables as dict, :meth:`get_exported` can be used.
332 The load name of the template owning this context.
334 .. attribute:: blocks
336 A dict with the current mapping of blocks in the template. The keys
337 in this dict are the names of the blocks, and the values a list of
338 blocks registered. The last item in each list is the current active
339 block (latest in the inheritance chain).
341 .. automethod:: jinja2.runtime.Context.call(callable, \*args, \**kwargs)
344 .. admonition:: Implementation
346 Context is immutable for the same reason Python's frame locals are
347 immutable inside functions. Both Jinja2 and Python are not using the
348 context / frame locals as data storage for variables but only as primary
351 When a template accesses a variable the template does not define, Jinja2
352 looks up the variable in the context, after that the variable is treated
353 as if it was defined in the template.
361 Loaders are responsible for loading templates from a resource such as the
362 file system. The environment will keep the compiled modules in memory like
363 Python's `sys.modules`. Unlike `sys.modules` however this cache is limited in
364 size by default and templates are automatically reloaded.
365 All loaders are subclasses of :class:`BaseLoader`. If you want to create your
366 own loader, subclass :class:`BaseLoader` and override `get_source`.
368 .. autoclass:: jinja2.loaders.BaseLoader
369 :members: get_source, load
371 Here a list of the builtin loaders Jinja2 provides:
373 .. autoclass:: jinja2.loaders.FileSystemLoader
375 .. autoclass:: jinja2.loaders.PackageLoader
377 .. autoclass:: jinja2.loaders.DictLoader
379 .. autoclass:: jinja2.loaders.FunctionLoader
381 .. autoclass:: jinja2.loaders.PrefixLoader
383 .. autoclass:: jinja2.loaders.ChoiceLoader
389 These helper functions and classes are useful if you add custom filters or
390 functions to a Jinja2 environment.
392 .. autofunction:: jinja2.filters.environmentfilter
394 .. autofunction:: jinja2.filters.contextfilter
396 .. autofunction:: jinja2.utils.environmentfunction
398 .. autofunction:: jinja2.utils.contextfunction
400 .. function:: escape(s)
402 Convert the characters ``&``, ``<``, ``>``, ``'``, and ``"`` in string `s`
403 to HTML-safe sequences. Use this if you need to display text that might
404 contain such characters in HTML. This function will not escaped objects
405 that do have an HTML representation such as already escaped data.
407 The return value is a :class:`Markup` string.
409 .. autofunction:: jinja2.utils.clear_caches
411 .. autofunction:: jinja2.utils.is_undefined
413 .. autoclass:: jinja2.utils.Markup
419 .. autoexception:: jinja2.exceptions.TemplateError
421 .. autoexception:: jinja2.exceptions.UndefinedError
423 .. autoexception:: jinja2.exceptions.TemplateNotFound
425 .. autoexception:: jinja2.exceptions.TemplateSyntaxError
427 .. attribute:: message
429 The error message as utf-8 bytestring.
431 .. attribute:: lineno
433 The line number where the error occurred
437 The load name for the template as unicode string.
439 .. attribute:: filename
441 The filename that loaded the template as bytestring in the encoding
442 of the file system (most likely utf-8 or mbcs on Windows systems).
444 The reason why the filename and error message are bytestrings and not
445 unicode strings is that Python 2.x is not using unicode for exceptions
446 and tracebacks as well as the compiler. This will change with Python 3.
448 .. autoexception:: jinja2.exceptions.TemplateAssertionError
456 Custom filters are just regular Python functions that take the left side of
457 the filter as first argument and the the arguments passed to the filter as
458 extra arguments or keyword arguments.
460 For example in the filter ``{{ 42|myfilter(23) }}`` the function would be
461 called with ``myfilter(42, 23)``. Here for example a simple filter that can
462 be applied to datetime objects to format them::
464 def datetimeformat(value, format='%H:%M / %d-%m-%Y'):
465 return value.strftime(format)
467 You can register it on the template environment by updating the
468 :attr:`~Environment.filters` dict on the environment::
470 environment.filters['datetimeformat'] = datetimeformat
472 Inside the template it can then be used as follows:
474 .. sourcecode:: jinja
476 written on: {{ article.pub_date|datetimeformat }}
477 publication date: {{ article.pub_date|datetimeformat('%d-%m-%Y') }}
479 Filters can also be passed the current template context or environment. This
480 is useful if a filters wants to return an undefined value or check the current
481 :attr:`~Environment.autoescape` setting. For this purpose two decorators
482 exist: :func:`environmentfilter` and :func:`contextfilter`.
484 Here a small example filter that breaks a text into HTML line breaks and
485 paragraphs and marks the return value as safe HTML string if autoescaping is
489 from jinja2 import environmentfilter, Markup, escape
491 _paragraph_re = re.compile(r'(?:\r\n|\r|\n){2,}')
494 def nl2br(environment, value):
495 result = u'\n\n'.join(u'<p>%s</p>' % p.replace('\n', '<br>\n')
496 for p in _paragraph_re.split(escape(value)))
497 if environment.autoescape:
498 result = Markup(result)
501 Context filters work the same just that the first argument is the current
502 active :class:`Context` rather then the environment.
510 Tests work like filters just that there is no way for a filter to get access
511 to the environment or context and that they can't be chained. The return
512 value of a filter should be `True` or `False`. The purpose of a filter is to
513 give the template designers the possibility to perform type and conformability
516 Here a simple filter that checks if a variable is a prime number::
523 for i in xrange(2, int(math.ceil(math.sqrt(n))) + 1):
529 You can register it on the template environment by updating the
530 :attr:`~Environment.tests` dict on the environment::
532 environment.tests['prime'] = is_prime
534 A template designer can then use the test like this:
536 .. sourcecode:: jinja
541 42 is not a prime number
545 .. _global-namespace:
550 Variables stored in the :attr:`Environment.globals` dict are special as they
551 are available for imported templates too, even if they are imported without
552 context. This is the place where you can put variables and functions
553 that should be available all the time. Additionally :attr:`Template.globals`
554 exist that are variables available to a specific template that are available
555 to all :meth:`~Template.render` calls.
563 The low level API exposes functionality that can be useful to understand some
564 implementation details, debugging purposes or advanced :ref:`extension
565 <jinja-extensions>` techniques. Unless you know exactly what you are doing we
566 don't recommend using any of those.
568 .. automethod:: Environment.lex
570 .. automethod:: Environment.parse
572 .. automethod:: Template.new_context
574 .. method:: Template.root_render_func(context)
576 This is the low level render function. It's passed a :class:`Context`
577 that has to be created by :meth:`new_context` of the same template or
578 a compatible template. This render function is generated by the
579 compiler from the template code and returns a generator that yields
582 If an exception in the template code happens the template engine will
583 not rewrite the exception but pass through the original one. As a
584 matter of fact this function should only be called from within a
585 :meth:`render` / :meth:`generate` / :meth:`stream` call.
587 .. attribute:: Template.blocks
589 A dict of block render functions. Each of these functions works exactly
590 like the :meth:`root_render_func` with the same limitations.
592 .. attribute:: Template.is_up_to_date
594 This attribute is `False` if there is a newer version of the template
595 available, otherwise `True`.
599 The low-level API is fragile. Future Jinja2 versions will not change it
600 in a backwards incompatible way but modifications in the Jinja core may
601 shine through. For example if Jinja2 introduces a new AST node in later
602 versions that may be returned by :meth:`~Environment.parse`.