836 lines
33 KiB
Plaintext
836 lines
33 KiB
Plaintext
====================================================
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The Django template language: For Python programmers
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====================================================
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This document explains the Django template system from a technical
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perspective -- how it works and how to extend it. If you're just looking for
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reference on the language syntax, see :doc:`/topics/templates`.
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If you're looking to use the Django template system as part of another
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application -- i.e., without the rest of the framework -- make sure to read
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the `configuration`_ section later in this document.
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.. _configuration: `configuring the template system in standalone mode`_
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Basics
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======
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A **template** is a text document, or a normal Python string, that is marked-up
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using the Django template language. A template can contain **block tags** or
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**variables**.
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A **block tag** is a symbol within a template that does something.
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This definition is deliberately vague. For example, a block tag can output
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content, serve as a control structure (an "if" statement or "for" loop), grab
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content from a database or enable access to other template tags.
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Block tags are surrounded by ``"{%"`` and ``"%}"``.
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Example template with block tags:
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.. code-block:: html+django
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{% if is_logged_in %}Thanks for logging in!{% else %}Please log in.{% endif %}
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A **variable** is a symbol within a template that outputs a value.
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Variable tags are surrounded by ``"{{"`` and ``"}}"``.
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Example template with variables:
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.. code-block:: html+django
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My first name is {{ first_name }}. My last name is {{ last_name }}.
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A **context** is a "variable name" -> "variable value" mapping that is passed
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to a template.
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A template **renders** a context by replacing the variable "holes" with values
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from the context and executing all block tags.
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Using the template system
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=========================
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.. class:: django.template.Template
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Using the template system in Python is a two-step process:
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* First, you compile the raw template code into a ``Template`` object.
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* Then, you call the ``render()`` method of the ``Template`` object with a
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given context.
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Compiling a string
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------------------
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The easiest way to create a ``Template`` object is by instantiating it
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directly. The class lives at :class:`django.template.Template`. The constructor
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takes one argument -- the raw template code::
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>>> from django.template import Template
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>>> t = Template("My name is {{ my_name }}.")
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>>> print t
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<django.template.Template instance>
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.. admonition:: Behind the scenes
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The system only parses your raw template code once -- when you create the
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``Template`` object. From then on, it's stored internally as a "node"
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structure for performance.
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Even the parsing itself is quite fast. Most of the parsing happens via a
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single call to a single, short, regular expression.
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Rendering a context
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-------------------
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.. method:: render(context)
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Once you have a compiled ``Template`` object, you can render a context -- or
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multiple contexts -- with it. The ``Context`` class lives at
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:class:`django.template.Context`, and the constructor takes two (optional)
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arguments:
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* A dictionary mapping variable names to variable values.
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* The name of the current application. This application name is used
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to help :ref:`resolve namespaced URLs<topics-http-reversing-url-namespaces>`.
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If you're not using namespaced URLs, you can ignore this argument.
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Call the ``Template`` object's ``render()`` method with the context to "fill" the
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template::
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>>> from django.template import Context, Template
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>>> t = Template("My name is {{ my_name }}.")
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>>> c = Context({"my_name": "Adrian"})
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>>> t.render(c)
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"My name is Adrian."
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>>> c = Context({"my_name": "Dolores"})
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>>> t.render(c)
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"My name is Dolores."
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Variable names must consist of any letter (A-Z), any digit (0-9), an underscore
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or a dot.
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Dots have a special meaning in template rendering. A dot in a variable name
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signifies a **lookup**. Specifically, when the template system encounters a
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dot in a variable name, it tries the following lookups, in this order:
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* Dictionary lookup. Example: ``foo["bar"]``
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* Attribute lookup. Example: ``foo.bar``
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* List-index lookup. Example: ``foo[bar]``
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The template system uses the first lookup type that works. It's short-circuit
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logic. Here are a few examples::
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>>> from django.template import Context, Template
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>>> t = Template("My name is {{ person.first_name }}.")
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>>> d = {"person": {"first_name": "Joe", "last_name": "Johnson"}}
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>>> t.render(Context(d))
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"My name is Joe."
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>>> class PersonClass: pass
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>>> p = PersonClass()
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>>> p.first_name = "Ron"
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>>> p.last_name = "Nasty"
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>>> t.render(Context({"person": p}))
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"My name is Ron."
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>>> t = Template("The first stooge in the list is {{ stooges.0 }}.")
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>>> c = Context({"stooges": ["Larry", "Curly", "Moe"]})
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>>> t.render(c)
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"The first stooge in the list is Larry."
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If any part of the variable is callable, the template system will try calling
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it. Example::
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>>> class PersonClass2:
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... def name(self):
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... return "Samantha"
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>>> t = Template("My name is {{ person.name }}.")
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>>> t.render(Context({"person": PersonClass2}))
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"My name is Samantha."
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.. versionchanged:: 1.3
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Previously, only variables that originated with an attribute lookup would
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be called by the template system. This change was made for consistency
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across lookup types.
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Callable variables are slightly more complex than variables which only require
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straight lookups. Here are some things to keep in mind:
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* If the variable raises an exception when called, the exception will be
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propagated, unless the exception has an attribute
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``silent_variable_failure`` whose value is ``True``. If the exception
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*does* have a ``silent_variable_failure`` attribute whose value is
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``True``, the variable will render as an empty string. Example::
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>>> t = Template("My name is {{ person.first_name }}.")
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>>> class PersonClass3:
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... def first_name(self):
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... raise AssertionError, "foo"
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>>> p = PersonClass3()
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>>> t.render(Context({"person": p}))
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Traceback (most recent call last):
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...
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AssertionError: foo
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>>> class SilentAssertionError(Exception):
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... silent_variable_failure = True
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>>> class PersonClass4:
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... def first_name(self):
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... raise SilentAssertionError
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>>> p = PersonClass4()
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>>> t.render(Context({"person": p}))
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"My name is ."
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Note that :exc:`django.core.exceptions.ObjectDoesNotExist`, which is the
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base class for all Django database API ``DoesNotExist`` exceptions, has
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``silent_variable_failure = True``. So if you're using Django templates
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with Django model objects, any ``DoesNotExist`` exception will fail
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silently.
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* A variable can only be called if it has no required arguments. Otherwise,
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the system will return an empty string.
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* Obviously, there can be side effects when calling some variables, and
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it'd be either foolish or a security hole to allow the template system
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to access them.
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A good example is the :meth:`~django.db.models.Model.delete` method on
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each Django model object. The template system shouldn't be allowed to do
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something like this::
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I will now delete this valuable data. {{ data.delete }}
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To prevent this, set an ``alters_data`` attribute on the callable
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variable. The template system won't call a variable if it has
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``alters_data=True`` set. The dynamically-generated
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:meth:`~django.db.models.Model.delete` and
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:meth:`~django.db.models.Model.save` methods on Django model objects get
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``alters_data=True`` automatically. Example::
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def sensitive_function(self):
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self.database_record.delete()
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sensitive_function.alters_data = True
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.. _invalid-template-variables:
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How invalid variables are handled
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Generally, if a variable doesn't exist, the template system inserts the
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value of the :setting:`TEMPLATE_STRING_IF_INVALID` setting, which is set to
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``''`` (the empty string) by default.
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Filters that are applied to an invalid variable will only be applied if
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:setting:`TEMPLATE_STRING_IF_INVALID` is set to ``''`` (the empty string). If
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:setting:`TEMPLATE_STRING_IF_INVALID` is set to any other value, variable
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filters will be ignored.
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This behavior is slightly different for the ``if``, ``for`` and ``regroup``
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template tags. If an invalid variable is provided to one of these template
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tags, the variable will be interpreted as ``None``. Filters are always
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applied to invalid variables within these template tags.
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If :setting:`TEMPLATE_STRING_IF_INVALID` contains a ``'%s'``, the format marker will
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be replaced with the name of the invalid variable.
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.. admonition:: For debug purposes only!
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While :setting:`TEMPLATE_STRING_IF_INVALID` can be a useful debugging tool,
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it is a bad idea to turn it on as a 'development default'.
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Many templates, including those in the Admin site, rely upon the
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silence of the template system when a non-existent variable is
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encountered. If you assign a value other than ``''`` to
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:setting:`TEMPLATE_STRING_IF_INVALID`, you will experience rendering
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problems with these templates and sites.
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Generally, :setting:`TEMPLATE_STRING_IF_INVALID` should only be enabled
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in order to debug a specific template problem, then cleared
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once debugging is complete.
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Playing with Context objects
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----------------------------
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.. class:: django.template.Context
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Most of the time, you'll instantiate ``Context`` objects by passing in a
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fully-populated dictionary to ``Context()``. But you can add and delete items
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from a ``Context`` object once it's been instantiated, too, using standard
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dictionary syntax::
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>>> c = Context({"foo": "bar"})
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>>> c['foo']
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'bar'
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>>> del c['foo']
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>>> c['foo']
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''
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>>> c['newvariable'] = 'hello'
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>>> c['newvariable']
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'hello'
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.. method:: pop()
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.. method:: push()
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.. exception:: django.template.ContextPopException
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A ``Context`` object is a stack. That is, you can ``push()`` and ``pop()`` it.
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If you ``pop()`` too much, it'll raise
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``django.template.ContextPopException``::
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>>> c = Context()
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>>> c['foo'] = 'first level'
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>>> c.push()
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>>> c['foo'] = 'second level'
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>>> c['foo']
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'second level'
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>>> c.pop()
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>>> c['foo']
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'first level'
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>>> c['foo'] = 'overwritten'
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>>> c['foo']
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'overwritten'
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>>> c.pop()
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Traceback (most recent call last):
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...
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django.template.ContextPopException
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.. method:: update(other_dict)
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In addition to ``push()`` and ``pop()``, the ``Context``
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object also defines an ``update()`` method. This works like ``push()``
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but takes a dictionary as an argument and pushes that dictionary onto
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the stack instead of an empty one.
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>>> c = Context()
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>>> c['foo'] = 'first level'
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>>> c.update({'foo': 'updated'})
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{'foo': 'updated'}
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>>> c['foo']
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'updated'
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>>> c.pop()
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{'foo': 'updated'}
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>>> c['foo']
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'first level'
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Using a ``Context`` as a stack comes in handy in some custom template tags, as
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you'll see below.
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.. _subclassing-context-requestcontext:
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Subclassing Context: RequestContext
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-----------------------------------
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.. class:: django.template.RequestContext
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Django comes with a special ``Context`` class,
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``django.template.RequestContext``, that acts slightly differently than the
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normal ``django.template.Context``. The first difference is that it takes an
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:class:`~django.http.HttpRequest` as its first argument. For example::
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c = RequestContext(request, {
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'foo': 'bar',
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})
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The second difference is that it automatically populates the context with a few
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variables, according to your :setting:`TEMPLATE_CONTEXT_PROCESSORS` setting.
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The :setting:`TEMPLATE_CONTEXT_PROCESSORS` setting is a tuple of callables --
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called **context processors** -- that take a request object as their argument
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and return a dictionary of items to be merged into the context. By default,
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:setting:`TEMPLATE_CONTEXT_PROCESSORS` is set to::
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("django.contrib.auth.context_processors.auth",
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"django.core.context_processors.debug",
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"django.core.context_processors.i18n",
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"django.core.context_processors.media",
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"django.core.context_processors.static",
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"django.contrib.messages.context_processors.messages")
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.. versionadded:: 1.2
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In addition to these, ``RequestContext`` always uses
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``django.core.context_processors.csrf``. This is a security
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related context processor required by the admin and other contrib apps, and,
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in case of accidental misconfiguration, it is deliberately hardcoded in and
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cannot be turned off by the :setting:`TEMPLATE_CONTEXT_PROCESSORS` setting.
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.. versionadded:: 1.2
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The ``'messages'`` context processor was added. For more information, see
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the :doc:`messages documentation </ref/contrib/messages>`.
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.. versionchanged:: 1.2
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The auth context processor was moved in this release from its old location
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``django.core.context_processors.auth`` to
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``django.contrib.auth.context_processors.auth``.
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Each processor is applied in order. That means, if one processor adds a
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variable to the context and a second processor adds a variable with the same
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name, the second will override the first. The default processors are explained
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below.
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.. admonition:: When context processors are applied
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When you use ``RequestContext``, the variables you supply directly
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are added first, followed any variables supplied by context
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processors. This means that a context processor may overwrite a
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variable you've supplied, so take care to avoid variable names
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which overlap with those supplied by your context processors.
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Also, you can give ``RequestContext`` a list of additional processors, using the
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optional, third positional argument, ``processors``. In this example, the
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``RequestContext`` instance gets a ``ip_address`` variable::
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def ip_address_processor(request):
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return {'ip_address': request.META['REMOTE_ADDR']}
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def some_view(request):
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# ...
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c = RequestContext(request, {
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'foo': 'bar',
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}, [ip_address_processor])
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return HttpResponse(t.render(c))
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.. note::
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If you're using Django's ``render_to_response()`` shortcut to populate a
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template with the contents of a dictionary, your template will be passed a
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``Context`` instance by default (not a ``RequestContext``). To use a
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``RequestContext`` in your template rendering, pass an optional third
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argument to ``render_to_response()``: a ``RequestContext``
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instance. Your code might look like this::
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def some_view(request):
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# ...
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return render_to_response('my_template.html',
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my_data_dictionary,
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context_instance=RequestContext(request))
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Here's what each of the default processors does:
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django.contrib.auth.context_processors.auth
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains this processor, every
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``RequestContext`` will contain these three variables:
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* ``user`` -- An ``auth.User`` instance representing the currently
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logged-in user (or an ``AnonymousUser`` instance, if the client isn't
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logged in).
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* ``messages`` -- A list of messages (as strings) that have been set
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via the :doc:`messages framework </ref/contrib/messages>`.
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* ``perms`` -- An instance of
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``django.core.context_processors.PermWrapper``, representing the
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permissions that the currently logged-in user has.
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.. versionchanged:: 1.2
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This context processor was moved in this release from
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``django.core.context_processors.auth`` to its current location.
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.. versionchanged:: 1.2
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Prior to version 1.2, the ``messages`` variable was a lazy accessor for
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``user.get_and_delete_messages()``. It has been changed to include any
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messages added via the :doc:`messages framework </ref/contrib/messages>`.
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django.core.context_processors.debug
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains this processor, every
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``RequestContext`` will contain these two variables -- but only if your
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:setting:`DEBUG` setting is set to ``True`` and the request's IP address
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(``request.META['REMOTE_ADDR']``) is in the :setting:`INTERNAL_IPS` setting:
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* ``debug`` -- ``True``. You can use this in templates to test whether
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you're in :setting:`DEBUG` mode.
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* ``sql_queries`` -- A list of ``{'sql': ..., 'time': ...}`` dictionaries,
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representing every SQL query that has happened so far during the request
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and how long it took. The list is in order by query.
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django.core.context_processors.i18n
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains this processor, every
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``RequestContext`` will contain these two variables:
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* ``LANGUAGES`` -- The value of the :setting:`LANGUAGES` setting.
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* ``LANGUAGE_CODE`` -- ``request.LANGUAGE_CODE``, if it exists. Otherwise,
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the value of the :setting:`LANGUAGE_CODE` setting.
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See :doc:`/topics/i18n/index` for more.
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django.core.context_processors.media
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains this processor, every
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``RequestContext`` will contain a variable ``MEDIA_URL``, providing the
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value of the :setting:`MEDIA_URL` setting.
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django.core.context_processors.static
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. versionadded:: 1.3
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If :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains this processor, every
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``RequestContext`` will contain a variable ``STATIC_URL``, providing the
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value of the :setting:`STATIC_URL` setting.
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django.core.context_processors.csrf
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. versionadded:: 1.2
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This processor adds a token that is needed by the ``csrf_token`` template tag
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for protection against :doc:`Cross Site Request Forgeries </ref/contrib/csrf>`.
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django.core.context_processors.request
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains this processor, every
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``RequestContext`` will contain a variable ``request``, which is the current
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:class:`~django.http.HttpRequest`. Note that this processor is not enabled by default;
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you'll have to activate it.
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django.contrib.messages.context_processors.messages
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains this processor, every
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``RequestContext`` will contain a single additional variable:
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* ``messages`` -- A list of messages (as strings) that have been set
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via the user model (using ``user.message_set.create``) or through
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the :doc:`messages framework </ref/contrib/messages>`.
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.. versionadded:: 1.2
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This template context variable was previously supplied by the ``'auth'``
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context processor. For backwards compatibility the ``'auth'`` context
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processor will continue to supply the ``messages`` variable until Django
|
|
1.4. If you use the ``messages`` variable, your project will work with
|
|
either (or both) context processors, but it is recommended to add
|
|
``django.contrib.messages.context_processors.messages`` so your project
|
|
will be prepared for the future upgrade.
|
|
|
|
Writing your own context processors
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
A context processor has a very simple interface: It's just a Python function
|
|
that takes one argument, an :class:`~django.http.HttpRequest` object, and
|
|
returns a dictionary that gets added to the template context. Each context
|
|
processor *must* return a dictionary.
|
|
|
|
Custom context processors can live anywhere in your code base. All Django cares
|
|
about is that your custom context processors are pointed-to by your
|
|
:setting:`TEMPLATE_CONTEXT_PROCESSORS` setting.
|
|
|
|
Loading templates
|
|
-----------------
|
|
|
|
Generally, you'll store templates in files on your filesystem rather than using
|
|
the low-level ``Template`` API yourself. Save templates in a directory
|
|
specified as a **template directory**.
|
|
|
|
Django searches for template directories in a number of places, depending on
|
|
your template-loader settings (see "Loader types" below), but the most basic
|
|
way of specifying template directories is by using the :setting:`TEMPLATE_DIRS`
|
|
setting.
|
|
|
|
The TEMPLATE_DIRS setting
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Tell Django what your template directories are by using the
|
|
:setting:`TEMPLATE_DIRS` setting in your settings file. This should be set to a
|
|
list or tuple of strings that contain full paths to your template
|
|
directory(ies). Example::
|
|
|
|
TEMPLATE_DIRS = (
|
|
"/home/html/templates/lawrence.com",
|
|
"/home/html/templates/default",
|
|
)
|
|
|
|
Your templates can go anywhere you want, as long as the directories and
|
|
templates are readable by the Web server. They can have any extension you want,
|
|
such as ``.html`` or ``.txt``, or they can have no extension at all.
|
|
|
|
Note that these paths should use Unix-style forward slashes, even on Windows.
|
|
|
|
.. _ref-templates-api-the-python-api:
|
|
|
|
The Python API
|
|
~~~~~~~~~~~~~~
|
|
|
|
Django has two ways to load templates from files:
|
|
|
|
.. function:: django.template.loader.get_template(template_name)
|
|
|
|
``get_template`` returns the compiled template (a ``Template`` object) for
|
|
the template with the given name. If the template doesn't exist, it raises
|
|
``django.template.TemplateDoesNotExist``.
|
|
|
|
.. function:: django.template.loader.select_template(template_name_list)
|
|
|
|
``select_template`` is just like ``get_template``, except it takes a list
|
|
of template names. Of the list, it returns the first template that exists.
|
|
|
|
For example, if you call ``get_template('story_detail.html')`` and have the
|
|
above :setting:`TEMPLATE_DIRS` setting, here are the files Django will look for,
|
|
in order:
|
|
|
|
* ``/home/html/templates/lawrence.com/story_detail.html``
|
|
* ``/home/html/templates/default/story_detail.html``
|
|
|
|
If you call ``select_template(['story_253_detail.html', 'story_detail.html'])``,
|
|
here's what Django will look for:
|
|
|
|
* ``/home/html/templates/lawrence.com/story_253_detail.html``
|
|
* ``/home/html/templates/default/story_253_detail.html``
|
|
* ``/home/html/templates/lawrence.com/story_detail.html``
|
|
* ``/home/html/templates/default/story_detail.html``
|
|
|
|
When Django finds a template that exists, it stops looking.
|
|
|
|
.. admonition:: Tip
|
|
|
|
You can use ``select_template()`` for super-flexible "templatability." For
|
|
example, if you've written a news story and want some stories to have
|
|
custom templates, use something like
|
|
``select_template(['story_%s_detail.html' % story.id, 'story_detail.html'])``.
|
|
That'll allow you to use a custom template for an individual story, with a
|
|
fallback template for stories that don't have custom templates.
|
|
|
|
Using subdirectories
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
|
|
It's possible -- and preferable -- to organize templates in subdirectories of
|
|
the template directory. The convention is to make a subdirectory for each
|
|
Django app, with subdirectories within those subdirectories as needed.
|
|
|
|
Do this for your own sanity. Storing all templates in the root level of a
|
|
single directory gets messy.
|
|
|
|
To load a template that's within a subdirectory, just use a slash, like so::
|
|
|
|
get_template('news/story_detail.html')
|
|
|
|
Using the same :setting:`TEMPLATE_DIRS` setting from above, this example
|
|
``get_template()`` call will attempt to load the following templates:
|
|
|
|
* ``/home/html/templates/lawrence.com/news/story_detail.html``
|
|
* ``/home/html/templates/default/news/story_detail.html``
|
|
|
|
.. _template-loaders:
|
|
|
|
Loader types
|
|
~~~~~~~~~~~~
|
|
|
|
By default, Django uses a filesystem-based template loader, but Django comes
|
|
with a few other template loaders, which know how to load templates from other
|
|
sources.
|
|
|
|
Some of these other loaders are disabled by default, but you can activate them
|
|
by editing your :setting:`TEMPLATE_LOADERS` setting. :setting:`TEMPLATE_LOADERS`
|
|
should be a tuple of strings, where each string represents a template loader
|
|
class. Here are the template loaders that come with Django:
|
|
|
|
.. versionchanged:: 1.2
|
|
Template loaders were based on callables (usually functions) before Django
|
|
1.2, starting with the 1.2 release there is a new class-based API, all the
|
|
loaders described below implement this new API.
|
|
|
|
``django.template.loaders.filesystem.Loader``
|
|
Loads templates from the filesystem, according to :setting:`TEMPLATE_DIRS`.
|
|
This loader is enabled by default.
|
|
|
|
``django.template.loaders.app_directories.Loader``
|
|
Loads templates from Django apps on the filesystem. For each app in
|
|
:setting:`INSTALLED_APPS`, the loader looks for a ``templates``
|
|
subdirectory. If the directory exists, Django looks for templates in there.
|
|
|
|
This means you can store templates with your individual apps. This also
|
|
makes it easy to distribute Django apps with default templates.
|
|
|
|
For example, for this setting::
|
|
|
|
INSTALLED_APPS = ('myproject.polls', 'myproject.music')
|
|
|
|
...then ``get_template('foo.html')`` will look for templates in these
|
|
directories, in this order:
|
|
|
|
* ``/path/to/myproject/polls/templates/foo.html``
|
|
* ``/path/to/myproject/music/templates/foo.html``
|
|
|
|
Note that the loader performs an optimization when it is first imported: It
|
|
caches a list of which :setting:`INSTALLED_APPS` packages have a
|
|
``templates`` subdirectory.
|
|
|
|
This loader is enabled by default.
|
|
|
|
``django.template.loaders.eggs.Loader``
|
|
Just like ``app_directories`` above, but it loads templates from Python
|
|
eggs rather than from the filesystem.
|
|
|
|
This loader is disabled by default.
|
|
|
|
``django.template.loaders.cached.Loader``
|
|
By default, the templating system will read and compile your templates every
|
|
time they need to be rendered. While the Django templating system is quite
|
|
fast, the overhead from reading and compiling templates can add up.
|
|
|
|
The cached template loader is a class-based loader that you configure with
|
|
a list of other loaders that it should wrap. The wrapped loaders are used to
|
|
locate unknown templates when they are first encountered. The cached loader
|
|
then stores the compiled ``Template`` in memory. The cached ``Template``
|
|
instance is returned for subsequent requests to load the same template.
|
|
|
|
For example, to enable template caching with the ``filesystem`` and
|
|
``app_directories`` template loaders you might use the following settings::
|
|
|
|
TEMPLATE_LOADERS = (
|
|
('django.template.loaders.cached.Loader', (
|
|
'django.template.loaders.filesystem.Loader',
|
|
'django.template.loaders.app_directories.Loader',
|
|
)),
|
|
)
|
|
|
|
.. note::
|
|
All of the built-in Django template tags are safe to use with the cached
|
|
loader, but if you're using custom template tags that come from third
|
|
party packages, or that you wrote yourself, you should ensure that the
|
|
``Node`` implementation for each tag is thread-safe. For more
|
|
information, see
|
|
:ref:`template tag thread safety considerations<template_tag_thread_safety>`.
|
|
|
|
This loader is disabled by default.
|
|
|
|
Django uses the template loaders in order according to the
|
|
:setting:`TEMPLATE_LOADERS` setting. It uses each loader until a loader finds a
|
|
match.
|
|
|
|
The ``render_to_string`` shortcut
|
|
===================================
|
|
|
|
.. function:: django.template.loader.render_to_string(template_name, dictionary=None, context_instance=None)
|
|
|
|
To cut down on the repetitive nature of loading and rendering
|
|
templates, Django provides a shortcut function which largely
|
|
automates the process: ``render_to_string()`` in
|
|
:mod:`django.template.loader`, which loads a template, renders it and
|
|
returns the resulting string::
|
|
|
|
from django.template.loader import render_to_string
|
|
rendered = render_to_string('my_template.html', { 'foo': 'bar' })
|
|
|
|
The ``render_to_string`` shortcut takes one required argument --
|
|
``template_name``, which should be the name of the template to load
|
|
and render (or a list of template names, in which case Django will use
|
|
the first template in the list that exists) -- and two optional arguments:
|
|
|
|
dictionary
|
|
A dictionary to be used as variables and values for the
|
|
template's context. This can also be passed as the second
|
|
positional argument.
|
|
|
|
context_instance
|
|
An instance of ``Context`` or a subclass (e.g., an instance of
|
|
``RequestContext``) to use as the template's context. This can
|
|
also be passed as the third positional argument.
|
|
|
|
See also the :func:`~django.shortcuts.render_to_response()` shortcut, which
|
|
calls ``render_to_string`` and feeds the result into an :class:`~django.http.HttpResponse`
|
|
suitable for returning directly from a view.
|
|
|
|
Configuring the template system in standalone mode
|
|
==================================================
|
|
|
|
.. note::
|
|
|
|
This section is only of interest to people trying to use the template
|
|
system as an output component in another application. If you're using the
|
|
template system as part of a Django application, nothing here applies to
|
|
you.
|
|
|
|
Normally, Django will load all the configuration information it needs from its
|
|
own default configuration file, combined with the settings in the module given
|
|
in the :envvar:`DJANGO_SETTINGS_MODULE` environment variable. But if you're
|
|
using the template system independently of the rest of Django, the environment
|
|
variable approach isn't very convenient, because you probably want to configure
|
|
the template system in line with the rest of your application rather than
|
|
dealing with settings files and pointing to them via environment variables.
|
|
|
|
To solve this problem, you need to use the manual configuration option described
|
|
in :ref:`settings-without-django-settings-module`. Simply import the appropriate
|
|
pieces of the templating system and then, *before* you call any of the
|
|
templating functions, call :func:`django.conf.settings.configure()` with any
|
|
settings you wish to specify. You might want to consider setting at least
|
|
:setting:`TEMPLATE_DIRS` (if you're going to use template loaders),
|
|
:setting:`DEFAULT_CHARSET` (although the default of ``utf-8`` is probably fine)
|
|
and :setting:`TEMPLATE_DEBUG`. All available settings are described in the
|
|
:doc:`settings documentation </ref/settings>`, and any setting starting with
|
|
``TEMPLATE_`` is of obvious interest.
|
|
|
|
.. _topic-template-alternate-language:
|
|
|
|
Using an alternative template language
|
|
======================================
|
|
|
|
.. versionadded:: 1.2
|
|
|
|
The Django ``Template`` and ``Loader`` classes implement a simple API for
|
|
loading and rendering templates. By providing some simple wrapper classes that
|
|
implement this API we can use third party template systems like `Jinja2
|
|
<http://jinja.pocoo.org/2/>`_ or `Cheetah <http://www.cheetahtemplate.org/>`_. This
|
|
allows us to use third-party template libraries without giving up useful Django
|
|
features like the Django ``Context`` object and handy shortcuts like
|
|
``render_to_response()``.
|
|
|
|
The core component of the Django templating system is the ``Template`` class.
|
|
This class has a very simple interface: it has a constructor that takes a single
|
|
positional argument specifying the template string, and a ``render()`` method
|
|
that takes a :class:`~django.template.Context` object and returns a string
|
|
containing the rendered response.
|
|
|
|
Suppose we're using a template language that defines a ``Template`` object with
|
|
a ``render()`` method that takes a dictionary rather than a ``Context`` object.
|
|
We can write a simple wrapper that implements the Django ``Template`` interface::
|
|
|
|
import some_template_language
|
|
class Template(some_template_language.Template):
|
|
def render(self, context):
|
|
# flatten the Django Context into a single dictionary.
|
|
context_dict = {}
|
|
for d in context.dicts:
|
|
context_dict.update(d)
|
|
return super(Template, self).render(context_dict)
|
|
|
|
That's all that's required to make our fictional ``Template`` class compatible
|
|
with the Django loading and rendering system!
|
|
|
|
The next step is to write a ``Loader`` class that returns instances of our custom
|
|
template class instead of the default :class:`~django.template.Template`. Custom ``Loader``
|
|
classes should inherit from ``django.template.loader.BaseLoader`` and override
|
|
the ``load_template_source()`` method, which takes a ``template_name`` argument,
|
|
loads the template from disk (or elsewhere), and returns a tuple:
|
|
``(template_string, template_origin)``.
|
|
|
|
The ``load_template()`` method of the ``Loader`` class retrieves the template
|
|
string by calling ``load_template_source()``, instantiates a ``Template`` from
|
|
the template source, and returns a tuple: ``(template, template_origin)``. Since
|
|
this is the method that actually instantiates the ``Template``, we'll need to
|
|
override it to use our custom template class instead. We can inherit from the
|
|
builtin :class:`django.template.loaders.app_directories.Loader` to take advantage
|
|
of the ``load_template_source()`` method implemented there::
|
|
|
|
from django.template.loaders import app_directories
|
|
class Loader(app_directories.Loader):
|
|
is_usable = True
|
|
|
|
def load_template(self, template_name, template_dirs=None):
|
|
source, origin = self.load_template_source(template_name, template_dirs)
|
|
template = Template(source)
|
|
return template, origin
|
|
|
|
Finally, we need to modify our project settings, telling Django to use our custom
|
|
loader. Now we can write all of our templates in our alternative template
|
|
language while continuing to use the rest of the Django templating system.
|