.. _renderers_chapter: Renderers ========= A view callable needn't *always* return a :term:`Response` object. If a view happens to return something which does not implement the Pyramid Response interface, :app:`Pyramid` will attempt to use a :term:`renderer` to construct a response. For example: .. code-block:: python :linenos: from pyramid.view import view_config @view_config(renderer='json') def hello_world(request): return {'content':'Hello!'} The above example returns a *dictionary* from the view callable. A dictionary does not implement the Pyramid response interface, so you might believe that this example would fail. However, since a ``renderer`` is associated with the view callable through its :term:`view configuration` (in this case, using a ``renderer`` argument passed to :func:`~pyramid.view.view_config`), if the view does *not* return a Response object, the renderer will attempt to convert the result of the view to a response on the developer's behalf. Of course, if no renderer is associated with a view's configuration, returning anything except an object which implements the Response interface will result in an error. And, if a renderer *is* used, whatever is returned by the view must be compatible with the particular kind of renderer used, or an error may occur during view invocation. One exception exists: it is *always* OK to return a Response object, even when a ``renderer`` is configured. In such cases, the renderer is bypassed entirely. Various types of renderers exist, including serialization renderers and renderers which use templating systems. .. index:: single: renderer single: view renderer .. _views_which_use_a_renderer: Writing View Callables Which Use a Renderer ------------------------------------------- As we've seen, a view callable needn't always return a Response object. Instead, it may return an arbitrary Python object, with the expectation that a :term:`renderer` will convert that object into a response instance on your behalf. Some renderers use a templating system, while other renderers use object serialization techniques. In practice, renderers obtain application data values from Python dictionaries so, in practice, view callables which use renderers return Python dictionaries. View callables can :ref:`explicitly call ` renderers, but typically don't. Instead view configuration declares the renderer used to render a view callable's results. This is done with the ``renderer`` attribute. For example, this call to :meth:`~pyramid.config.Configurator.add_view` associates the ``json`` renderer with a view callable: .. code-block:: python config.add_view('myproject.views.my_view', renderer='json') When this configuration is added to an application, the ``myproject.views.my_view`` view callable will now use a ``json`` renderer, which renders view return values to a :term:`JSON` response serialization. Pyramid defines several :ref:`built_in_renderers`, and additional renderers can be added by developers to the system as necessary. See :ref:`adding_and_overriding_renderers`. Views which use a renderer and return a non-Response value can vary non-body response attributes (such as headers and the HTTP status code) by attaching a property to the ``request.response`` attribute. See :ref:`request_response_attr`. As already mentioned, if the :term:`view callable` associated with a :term:`view configuration` returns a Response object (or its instance), any renderer associated with the view configuration is ignored, and the response is passed back to :app:`Pyramid` unchanged. For example: .. code-block:: python :linenos: from pyramid.response import Response from pyramid.view import view_config @view_config(renderer='json') def view(request): return Response('OK') # json renderer avoided Likewise for an :term:`HTTP exception` response: .. code-block:: python :linenos: from pyramid.httpexceptions import HTTPFound from pyramid.view import view_config @view_config(renderer='json') def view(request): return HTTPFound(location='http://example.com') # json renderer avoided You can of course also return the ``request.response`` attribute instead to avoid rendering: .. code-block:: python :linenos: from pyramid.view import view_config @view_config(renderer='json') def view(request): request.response.body = 'OK' return request.response # json renderer avoided .. index:: single: renderers (built-in) single: built-in renderers .. _built_in_renderers: Built-in Renderers ------------------ Several built-in renderers exist in :app:`Pyramid`. These renderers can be used in the ``renderer`` attribute of view configurations. .. note:: Bindings for officially supported templating languages can be found at :ref:`available_template_system_bindings`. .. index:: pair: renderer; string ``string``: String Renderer ~~~~~~~~~~~~~~~~~~~~~~~~~~~ The ``string`` renderer renders a view callable result to a string. If a view callable returns a non-Response object, and the ``string`` renderer is associated in that view's configuration, the result will be to run the object through the Python ``str`` function to generate a string. Here's an example of a view that returns a dictionary. If the ``string`` renderer is specified in the configuration for this view, the view will render the returned dictionary to the ``str()`` representation of the dictionary: .. code-block:: python :linenos: from pyramid.view import view_config @view_config(renderer='string') def hello_world(request): return {'content':'Hello!'} The body of the response returned by such a view will be a string representing the ``str()`` serialization of the return value: .. code-block:: python {'content': 'Hello!'} Views which use the string renderer can vary non-body response attributes by using the API of the ``request.response`` attribute. See :ref:`request_response_attr`. .. index:: pair: renderer; JSON .. _json_renderer: JSON Renderer ~~~~~~~~~~~~~ The ``json`` renderer renders view callable results to :term:`JSON`. By default, it passes the return value through the ``json.dumps`` standard library function, and wraps the result in a response object. It also sets the response content-type to ``application/json``. Here's an example of a view that returns a dictionary. Since the ``json`` renderer is specified in the configuration for this view, the view will render the returned dictionary to a JSON serialization: .. code-block:: python :linenos: from pyramid.view import view_config @view_config(renderer='json') def hello_world(request): return {'content':'Hello!'} The body of the response returned by such a view will be a string representing the JSON serialization of the return value: .. code-block:: python {"content": "Hello!"} The return value needn't be a dictionary, but the return value must contain values serializable by the configured serializer (by default ``json.dumps``). You can configure a view to use the JSON renderer by naming ``json`` as the ``renderer`` argument of a view configuration, e.g., by using :meth:`~pyramid.config.Configurator.add_view`: .. code-block:: python :linenos: config.add_view('myproject.views.hello_world', name='hello', context='myproject.resources.Hello', renderer='json') Views which use the JSON renderer can vary non-body response attributes by using the API of the ``request.response`` attribute. See :ref:`request_response_attr`. .. _json_serializing_custom_objects: Serializing Custom Objects ++++++++++++++++++++++++++ Some objects are not, by default, JSON-serializable (such as datetimes and other arbitrary Python objects). You can, however, register code that makes non-serializable objects serializable in two ways: - Define a ``__json__`` method on objects in your application. - For objects you don't "own", you can register a JSON renderer that knows about an *adapter* for that kind of object. Using a Custom ``__json__`` Method ********************************** Custom objects can be made easily JSON-serializable in Pyramid by defining a ``__json__`` method on the object's class. This method should return values natively JSON-serializable (such as ints, lists, dictionaries, strings, and so forth). It should accept a single additional argument, ``request``, which will be the active request object at render time. .. code-block:: python :linenos: from pyramid.view import view_config class MyObject(object): def __init__(self, x): self.x = x def __json__(self, request): return {'x':self.x} @view_config(renderer='json') def objects(request): return [MyObject(1), MyObject(2)] # the JSON value returned by ``objects`` will be: # [{"x": 1}, {"x": 2}] Using the ``add_adapter`` Method of a Custom JSON Renderer ********************************************************** If you aren't the author of the objects being serialized, it won't be possible (or at least not reasonable) to add a custom ``__json__`` method to their classes in order to influence serialization. If the object passed to the renderer is not a serializable type and has no ``__json__`` method, usually a :exc:`TypeError` will be raised during serialization. You can change this behavior by creating a custom JSON renderer and adding adapters to handle custom types. The renderer will attempt to adapt non-serializable objects using the registered adapters. A short example follows: .. code-block:: python :linenos: from pyramid.renderers import JSON if __name__ == '__main__': config = Configurator() json_renderer = JSON() def datetime_adapter(obj, request): return obj.isoformat() json_renderer.add_adapter(datetime.datetime, datetime_adapter) config.add_renderer('json', json_renderer) The ``add_adapter`` method should accept two arguments: the *class* of the object that you want this adapter to run for (in the example above, ``datetime.datetime``), and the adapter itself. The adapter should be a callable. It should accept two arguments: the object needing to be serialized and ``request``, which will be the current request object at render time. The adapter should raise a :exc:`TypeError` if it can't determine what to do with the object. See :class:`pyramid.renderers.JSON` and :ref:`adding_and_overriding_renderers` for more information. .. versionadded:: 1.4 Serializing custom objects. .. index:: pair: renderer; JSONP .. _jsonp_renderer: JSONP Renderer ~~~~~~~~~~~~~~ .. versionadded:: 1.1 :class:`pyramid.renderers.JSONP` is a `JSONP `_ renderer factory helper which implements a hybrid JSON/JSONP renderer. JSONP is useful for making cross-domain AJAX requests. Unlike other renderers, a JSONP renderer needs to be configured at startup time "by hand". Configure a JSONP renderer using the :meth:`pyramid.config.Configurator.add_renderer` method: .. code-block:: python from pyramid.config import Configurator from pyramid.renderers import JSONP config = Configurator() config.add_renderer('jsonp', JSONP(param_name='callback')) Once this renderer is registered via :meth:`~pyramid.config.Configurator.add_renderer` as above, you can use ``jsonp`` as the ``renderer=`` parameter to ``@view_config`` or :meth:`pyramid.config.Configurator.add_view`: .. code-block:: python from pyramid.view import view_config @view_config(renderer='jsonp') def myview(request): return {'greeting':'Hello world'} When a view is called that uses a JSONP renderer: - If there is a parameter in the request's HTTP query string (aka ``request.GET``) that matches the ``param_name`` of the registered JSONP renderer (by default, ``callback``), the renderer will return a JSONP response. - If there is no callback parameter in the request's query string, the renderer will return a "plain" JSON response. Javscript library AJAX functionality will help you make JSONP requests. For example, JQuery has a `getJSON function `_, and has equivalent (but more complicated) functionality in its `ajax function `_. For example (JavaScript): .. code-block:: javascript var api_url = 'http://api.geonames.org/timezoneJSON' + '?lat=38.301733840000004' + '&lng=-77.45869621' + '&username=fred' + '&callback=?'; jqhxr = $.getJSON(api_url); The string ``callback=?`` above in the ``url`` param to the JQuery ``getJSON`` function indicates to jQuery that the query should be made as a JSONP request; the ``callback`` parameter will be automatically filled in for you and used. The same custom-object serialization scheme defined used for a "normal" JSON renderer in :ref:`json_serializing_custom_objects` can be used when passing values to a JSONP renderer too. .. index:: single: response headers (from a renderer) single: renderer response headers .. _request_response_attr: Varying Attributes of Rendered Responses ---------------------------------------- Before a response constructed by a :term:`renderer` is returned to :app:`Pyramid`, several attributes of the request are examined which have the potential to influence response behavior. View callables that don't directly return a response should use the API of the :class:`pyramid.response.Response` attribute, available as ``request.response`` during their execution, to influence associated response behavior. For example, if you need to change the response status from within a view callable that uses a renderer, assign the ``status`` attribute to the ``response`` attribute of the request before returning a result: .. code-block:: python :linenos: from pyramid.view import view_config @view_config(name='gone', renderer='templates/gone.pt') def myview(request): request.response.status = '404 Not Found' return {'URL':request.URL} Note that mutations of ``request.response`` in views which return a Response object directly will have no effect unless the response object returned *is* ``request.response``. For example, the following example calls ``request.response.set_cookie``, but this call will have no effect because a different Response object is returned. .. code-block:: python :linenos: from pyramid.response import Response def view(request): request.response.set_cookie('abc', '123') # this has no effect return Response('OK') # because we're returning a different response If you mutate ``request.response`` and you'd like the mutations to have an effect, you must return ``request.response``: .. code-block:: python :linenos: def view(request): request.response.set_cookie('abc', '123') return request.response For more information on attributes of the request, see the API documentation in :ref:`request_module`. For more information on the API of ``request.response``, see :attr:`pyramid.request.Request.response`. .. _adding_and_overriding_renderers: Adding and Changing Renderers ----------------------------- New templating systems and serializers can be associated with :app:`Pyramid` renderer names. To this end, configuration declarations can be made which change an existing :term:`renderer factory`, and which add a new renderer factory. Renderers can be registered imperatively using the :meth:`pyramid.config.Configurator.add_renderer` API. For example, to add a renderer which renders views which have a ``renderer`` attribute that is a path that ends in ``.jinja2``: .. code-block:: python config.add_renderer('.jinja2', 'mypackage.MyJinja2Renderer') The first argument is the renderer name. The second argument is a reference to an implementation of a :term:`renderer factory` or a :term:`dotted Python name` referring to such an object. .. index:: pair: renderer; adding .. _adding_a_renderer: Adding a New Renderer ~~~~~~~~~~~~~~~~~~~~~ You may add a new renderer by creating and registering a :term:`renderer factory`. A renderer factory implementation should conform to the :class:`pyramid.interfaces.IRendererFactory` interface. It should be capable of creating an object that conforms to the :class:`pyramid.interfaces.IRenderer` interface. A typical class that follows this setup is as follows: .. code-block:: python :linenos: class RendererFactory: def __init__(self, info): """ Constructor: info will be an object having the following attributes: name (the renderer name), package (the package that was 'current' at the time the renderer was registered), type (the renderer type name), registry (the current application registry) and settings (the deployment settings dictionary). """ def __call__(self, value, system): """ Call the renderer implementation with the value and the system value passed in as arguments and return the result (a bytes or string object). The value is the return value of a view. The system value is a dictionary containing available system values (e.g., view, context, and request). """ The formal interface definition of the ``info`` object passed to a renderer factory constructor is available as :class:`pyramid.interfaces.IRendererInfo`. There are essentially two different kinds of renderer factories: - A renderer factory which expects to accept an :term:`asset specification`, or an absolute path, as the ``name`` attribute of the ``info`` object fed to its constructor. These renderer factories are registered with a ``name`` value that begins with a dot (``.``). These types of renderer factories usually relate to a file on the filesystem, such as a template. - A renderer factory which expects to accept a token that does not represent a filesystem path or an asset specification in the ``name`` attribute of the ``info`` object fed to its constructor. These renderer factories are registered with a ``name`` value that does not begin with a dot. These renderer factories are typically object serializers. .. sidebar:: Asset Specifications An asset specification is a colon-delimited identifier for an :term:`asset`. The colon separates a Python :term:`package` name from a package subpath. For example, the asset specification ``my.package:static/baz.css`` identifies the file named ``baz.css`` in the ``static`` subdirectory of the ``my.package`` Python :term:`package`. Here's an example of the registration of a simple renderer factory via :meth:`~pyramid.config.Configurator.add_renderer`, where ``config`` is an instance of :meth:`pyramid.config.Configurator`: .. code-block:: python config.add_renderer(name='amf', factory='my.package.MyAMFRenderer') Adding the above code to your application startup configuration will allow you to use the ``my.package.MyAMFRenderer`` renderer factory implementation in view configurations. Your application can use this renderer by specifying ``amf`` in the ``renderer`` attribute of a :term:`view configuration`: .. code-block:: python :linenos: from pyramid.view import view_config @view_config(renderer='amf') def myview(request): return {'Hello':'world'} At startup time, when a :term:`view configuration` is encountered which has a ``name`` attribute that does not contain a dot, the full ``name`` value is used to construct a renderer from the associated renderer factory. In this case, the view configuration will create an instance of an ``MyAMFRenderer`` for each view configuration which includes ``amf`` as its renderer value. The ``name`` passed to the ``MyAMFRenderer`` constructor will always be ``amf``. Here's an example of the registration of a more complicated renderer factory, which expects to be passed a filesystem path: .. code-block:: python config.add_renderer(name='.jinja2', factory='my.package.MyJinja2Renderer') Adding the above code to your application startup will allow you to use the ``my.package.MyJinja2Renderer`` renderer factory implementation in view configurations by referring to any ``renderer`` which *ends in* ``.jinja2`` in the ``renderer`` attribute of a :term:`view configuration`: .. code-block:: python :linenos: from pyramid.view import view_config @view_config(renderer='templates/mytemplate.jinja2') def myview(request): return {'Hello':'world'} When a :term:`view configuration` is encountered at startup time which has a ``name`` attribute that does contain a dot, the value of the name attribute is split on its final dot. The second element of the split is typically the filename extension. This extension is used to look up a renderer factory for the configured view. Then the value of ``renderer`` is passed to the factory to create a renderer for the view. In this case, the view configuration will create an instance of a ``MyJinja2Renderer`` for each view configuration which includes anything ending with ``.jinja2`` in its ``renderer`` value. The ``name`` passed to the ``MyJinja2Renderer`` constructor will be the full value that was set as ``renderer=`` in the view configuration. Adding a Default Renderer ~~~~~~~~~~~~~~~~~~~~~~~~~ To associate a *default* renderer with *all* view configurations (even ones which do not possess a ``renderer`` attribute), pass ``None`` as the ``name`` attribute to the renderer tag: .. code-block:: python config.add_renderer(None, 'mypackage.json_renderer_factory') .. index:: pair: renderer; changing Changing an Existing Renderer ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Pyramid supports overriding almost every aspect of its setup through its :ref:`Conflict Resolution ` mechanism. This means that, in most cases, overriding a renderer is as simple as using the :meth:`pyramid.config.Configurator.add_renderer` method to redefine the template extension. For example, if you would like to override the ``json`` renderer to specify a new renderer, you could do the following: .. code-block:: python json_renderer = pyramid.renderers.JSON() config.add_renderer('json', json_renderer) After doing this, any views registered with the ``json`` renderer will use the new renderer. .. index:: pair: renderer; overriding at runtime Overriding a Renderer at Runtime -------------------------------- .. warning:: This is an advanced feature, not typically used by "civilians". In some circumstances, it is necessary to instruct the system to ignore the static renderer declaration provided by the developer in view configuration, replacing the renderer with another *after a request starts*. For example, an "omnipresent" XML-RPC implementation that detects that the request is from an XML-RPC client might override a view configuration statement made by the user instructing the view to use a template renderer with one that uses an XML-RPC renderer. This renderer would produce an XML-RPC representation of the data returned by an arbitrary view callable. To use this feature, create a :class:`~pyramid.events.NewRequest` :term:`subscriber` which sniffs at the request data and which conditionally sets an ``override_renderer`` attribute on the request itself, which in turn is the *name* of a registered renderer. For example: .. code-block:: python :linenos: from pyramid.events import subscriber from pyramid.events import NewRequest @subscriber(NewRequest) def set_xmlrpc_params(event): request = event.request if (request.content_type == 'text/xml' and request.method == 'POST' and not 'soapaction' in request.headers and not 'x-pyramid-avoid-xmlrpc' in request.headers): params, method = parse_xmlrpc_request(request) request.xmlrpc_params, request.xmlrpc_method = params, method request.is_xmlrpc = True request.override_renderer = 'xmlrpc' return True The result of such a subscriber will be to replace any existing static renderer configured by the developer with a (notional, nonexistent) XML-RPC renderer, if the request appears to come from an XML-RPC client.