296 lines
11 KiB
Plaintext
296 lines
11 KiB
Plaintext
===========================================
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TemplateResponse and SimpleTemplateResponse
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===========================================
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.. module:: django.template.response
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:synopsis: Classes dealing with lazy-rendered HTTP responses.
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Standard :class:`~django.http.HttpResponse` objects are static structures.
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They are provided with a block of pre-rendered content at time of
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construction, and while that content can be modified, it isn't in a form that
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makes it easy to perform modifications.
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However, it can sometimes be beneficial to allow decorators or
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middleware to modify a response *after* it has been constructed by the
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view. For example, you may want to change the template that is used,
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or put additional data into the context.
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TemplateResponse provides a way to do just that. Unlike basic
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:class:`~django.http.HttpResponse` objects, TemplateResponse objects retain
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the details of the template and context that was provided by the view to
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compute the response. The final output of the response is not computed until
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it is needed, later in the response process.
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SimpleTemplateResponse objects
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==============================
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.. class:: SimpleTemplateResponse()
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Attributes
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----------
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.. attribute:: SimpleTemplateResponse.template_name
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The name of the template to be rendered. Accepts a backend-dependent
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template object (such as those returned by
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:func:`~django.template.loader.get_template()`), the name of a template,
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or a list of template names.
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Example: ``['foo.html', 'path/to/bar.html']``
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.. attribute:: SimpleTemplateResponse.context_data
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The context data to be used when rendering the template. It must be a
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:class:`dict`.
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Example: ``{'foo': 123}``
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.. attribute:: SimpleTemplateResponse.rendered_content
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The current rendered value of the response content, using the current
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template and context data.
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.. attribute:: SimpleTemplateResponse.is_rendered
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A boolean indicating whether the response content has been rendered.
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Methods
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-------
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.. method:: SimpleTemplateResponse.__init__(template, context=None, content_type=None, status=None, charset=None, using=None)
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Instantiates a :class:`~django.template.response.SimpleTemplateResponse`
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object with the given template, context, content type, HTTP status, and
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charset.
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``template``
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A backend-dependent template object (such as those returned by
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:func:`~django.template.loader.get_template()`), the name of a template,
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or a list of template names.
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``context``
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A :class:`dict` of values to add to the template context. By default,
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this is an empty dictionary.
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``content_type``
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The value included in the HTTP ``Content-Type`` header, including the
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MIME type specification and the character set encoding. If
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``content_type`` is specified, then its value is used. Otherwise,
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:setting:`DEFAULT_CONTENT_TYPE` is used.
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``status``
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The HTTP status code for the response.
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``charset``
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The charset in which the response will be encoded. If not given it will
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be extracted from ``content_type``, and if that is unsuccessful, the
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:setting:`DEFAULT_CHARSET` setting will be used.
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``using``
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The :setting:`NAME <TEMPLATES-NAME>` of a template engine to use for
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loading the template.
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.. method:: SimpleTemplateResponse.resolve_context(context)
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Preprocesses context data that will be used for rendering a template.
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Accepts a :class:`dict` of context data. By default, returns the same
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:class:`dict`.
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Override this method in order to customize the context.
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.. method:: SimpleTemplateResponse.resolve_template(template)
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Resolves the template instance to use for rendering. Accepts a
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backend-dependent template object (such as those returned by
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:func:`~django.template.loader.get_template()`), the name of a template,
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or a list of template names.
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Returns the backend-dependent template object instance to be rendered.
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Override this method in order to customize template loading.
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.. method:: SimpleTemplateResponse.add_post_render_callback()
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Add a callback that will be invoked after rendering has taken
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place. This hook can be used to defer certain processing
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operations (such as caching) until after rendering has occurred.
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If the :class:`~django.template.response.SimpleTemplateResponse`
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has already been rendered, the callback will be invoked
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immediately.
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When called, callbacks will be passed a single argument -- the
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rendered :class:`~django.template.response.SimpleTemplateResponse`
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instance.
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If the callback returns a value that is not ``None``, this will be
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used as the response instead of the original response object (and
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will be passed to the next post rendering callback etc.)
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.. method:: SimpleTemplateResponse.render()
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Sets ``response.content`` to the result obtained by
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:attr:`SimpleTemplateResponse.rendered_content`, runs all post-rendering
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callbacks, and returns the resulting response object.
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``render()`` will only have an effect the first time it is called. On
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subsequent calls, it will return the result obtained from the first call.
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TemplateResponse objects
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========================
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.. class:: TemplateResponse()
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``TemplateResponse`` is a subclass of
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:class:`~django.template.response.SimpleTemplateResponse` that knows about
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the current :class:`~django.http.HttpRequest`.
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Methods
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-------
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.. method:: TemplateResponse.__init__(request, template, context=None, content_type=None, status=None, charset=None, using=None)
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Instantiates a :class:`~django.template.response.TemplateResponse` object
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with the given request, template, context, content type, HTTP status, and
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charset.
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``request``
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An :class:`~django.http.HttpRequest` instance.
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``template``
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A backend-dependent template object (such as those returned by
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:func:`~django.template.loader.get_template()`), the name of a template,
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or a list of template names.
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``context``
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A :class:`dict` of values to add to the template context. By default,
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this is an empty dictionary.
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``content_type``
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The value included in the HTTP ``Content-Type`` header, including the
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MIME type specification and the character set encoding. If
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``content_type`` is specified, then its value is used. Otherwise,
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:setting:`DEFAULT_CONTENT_TYPE` is used.
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``status``
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The HTTP status code for the response.
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``charset``
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The charset in which the response will be encoded. If not given it will
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be extracted from ``content_type``, and if that is unsuccessful, the
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:setting:`DEFAULT_CHARSET` setting will be used.
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``using``
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The :setting:`NAME <TEMPLATES-NAME>` of a template engine to use for
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loading the template.
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The rendering process
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=====================
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Before a :class:`~django.template.response.TemplateResponse` instance can be
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returned to the client, it must be rendered. The rendering process takes the
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intermediate representation of template and context, and turns it into the
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final byte stream that can be served to the client.
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There are three circumstances under which a ``TemplateResponse`` will be
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rendered:
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* When the ``TemplateResponse`` instance is explicitly rendered, using
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the :meth:`SimpleTemplateResponse.render()` method.
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* When the content of the response is explicitly set by assigning
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``response.content``.
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* After passing through template response middleware, but before
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passing through response middleware.
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A ``TemplateResponse`` can only be rendered once. The first call to
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:meth:`SimpleTemplateResponse.render` sets the content of the response;
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subsequent rendering calls do not change the response content.
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However, when ``response.content`` is explicitly assigned, the
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change is always applied. If you want to force the content to be
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re-rendered, you can re-evaluate the rendered content, and assign
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the content of the response manually::
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# Set up a rendered TemplateResponse
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>>> from django.template.response import TemplateResponse
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>>> t = TemplateResponse(request, 'original.html', {})
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>>> t.render()
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>>> print(t.content)
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Original content
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# Re-rendering doesn't change content
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>>> t.template_name = 'new.html'
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>>> t.render()
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>>> print(t.content)
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Original content
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# Assigning content does change, no render() call required
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>>> t.content = t.rendered_content
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>>> print(t.content)
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New content
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Post-render callbacks
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---------------------
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Some operations -- such as caching -- cannot be performed on an
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unrendered template. They must be performed on a fully complete and
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rendered response.
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If you're using middleware, the solution is easy. Middleware provides
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multiple opportunities to process a response on exit from a view. If
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you put behavior in the Response middleware is guaranteed to execute
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after template rendering has taken place.
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However, if you're using a decorator, the same opportunities do not
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exist. Any behavior defined in a decorator is handled immediately.
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To compensate for this (and any other analogous use cases),
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:class:`TemplateResponse` allows you to register callbacks that will
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be invoked when rendering has completed. Using this callback, you can
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defer critical processing until a point where you can guarantee that
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rendered content will be available.
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To define a post-render callback, just define a function that takes
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a single argument -- response -- and register that function with
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the template response::
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from django.template.response import TemplateResponse
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def my_render_callback(response):
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# Do content-sensitive processing
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do_post_processing()
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def my_view(request):
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# Create a response
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response = TemplateResponse(request, 'mytemplate.html', {})
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# Register the callback
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response.add_post_render_callback(my_render_callback)
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# Return the response
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return response
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``my_render_callback()`` will be invoked after the ``mytemplate.html``
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has been rendered, and will be provided the fully rendered
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:class:`TemplateResponse` instance as an argument.
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If the template has already been rendered, the callback will be
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invoked immediately.
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Using TemplateResponse and SimpleTemplateResponse
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=================================================
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A :class:`TemplateResponse` object can be used anywhere that a normal
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:class:`django.http.HttpResponse` can be used. It can also be used as an
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alternative to calling :func:`~django.shortcuts.render()` or
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:func:`~django.shortcuts.render_to_response()`.
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For example, the following simple view returns a :class:`TemplateResponse`
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with a simple template and a context containing a queryset::
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from django.template.response import TemplateResponse
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def blog_index(request):
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return TemplateResponse(request, 'entry_list.html', {'entries': Entry.objects.all()})
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