.. index:: single: extending configuration .. _extconfig_narr: Extending Pyramid Configuration =============================== Pyramid allows you to extend its Configurator with custom directives. Custom directives can use other directives, they can add a custom :term:`action`, they can participate in :term:`conflict resolution`, and they can provide some number of :term:`introspectable` objects. .. index:: single: add_directive pair: configurator; adding directives .. _add_directive: Adding Methods to the Configurator via ``add_directive`` -------------------------------------------------------- Framework extension writers can add arbitrary methods to a :term:`Configurator` by using the :meth:`pyramid.config.Configurator.add_directive` method of the configurator. Using :meth:`~pyramid.config.Configurator.add_directive` makes it possible to extend a Pyramid configurator in arbitrary ways, and allows it to perform application-specific tasks more succinctly. The :meth:`~pyramid.config.Configurator.add_directive` method accepts two positional arguments: a method name and a callable object. The callable object is usually a function that takes the configurator instance as its first argument and accepts other arbitrary positional and keyword arguments. For example: .. code-block:: python :linenos: from pyramid.events import NewRequest from pyramid.config import Configurator def add_newrequest_subscriber(config, subscriber): config.add_subscriber(subscriber, NewRequest) if __name__ == '__main__': config = Configurator() config.add_directive('add_newrequest_subscriber', add_newrequest_subscriber) Once :meth:`~pyramid.config.Configurator.add_directive` is called, a user can then call the added directive by its given name as if it were a built-in method of the Configurator: .. code-block:: python :linenos: def mysubscriber(event): print(event.request) config.add_newrequest_subscriber(mysubscriber) A call to :meth:`~pyramid.config.Configurator.add_directive` is often "hidden" within an ``includeme`` function within a "frameworky" package meant to be included as per :ref:`including_configuration` via :meth:`~pyramid.config.Configurator.include`. For example, if you put this code in a package named ``pyramid_subscriberhelpers``: .. code-block:: python :linenos: def includeme(config): config.add_directive('add_newrequest_subscriber', add_newrequest_subscriber) The user of the add-on package ``pyramid_subscriberhelpers`` would then be able to install it and subsequently do: .. code-block:: python :linenos: def mysubscriber(event): print(event.request) from pyramid.config import Configurator config = Configurator() config.include('pyramid_subscriberhelpers') config.add_newrequest_subscriber(mysubscriber) Using ``config.action`` in a Directive -------------------------------------- If a custom directive can't do its work exclusively in terms of existing configurator methods (such as :meth:`pyramid.config.Configurator.add_subscriber` as above), the directive may need to make use of the :meth:`pyramid.config.Configurator.action` method. This method adds an entry to the list of "actions" that Pyramid will attempt to process when :meth:`pyramid.config.Configurator.commit` is called. An action is simply a dictionary that includes a :term:`discriminator`, possibly a callback function, and possibly other metadata used by Pyramid's action system. Here's an example directive which uses the "action" method: .. code-block:: python :linenos: def add_jammyjam(config, jammyjam): def register(): config.registry.jammyjam = jammyjam config.action('jammyjam', register) if __name__ == '__main__': config = Configurator() config.add_directive('add_jammyjam', add_jammyjam) Fancy, but what does it do? The action method accepts a number of arguments. In the above directive named ``add_jammyjam``, we call :meth:`~pyramid.config.Configurator.action` with two arguments: the string ``jammyjam`` is passed as the first argument named ``discriminator``, and the closure function named ``register`` is passed as the second argument named ``callable``. When the :meth:`~pyramid.config.Configurator.action` method is called, it appends an action to the list of pending configuration actions. All pending actions with the same discriminator value are potentially in conflict with one another (see :ref:`conflict_detection`). When the :meth:`~pyramid.config.Configurator.commit` method of the Configurator is called (either explicitly or as the result of calling :meth:`~pyramid.config.Configurator.make_wsgi_app`), conflicting actions are potentially automatically resolved as per :ref:`automatic_conflict_resolution`. If a conflict cannot be automatically resolved, a :exc:`pyramid.exceptions.ConfigurationConflictError` is raised and application startup is prevented. In our above example, therefore, if a consumer of our ``add_jammyjam`` directive did this: .. code-block:: python config.add_jammyjam('first') config.add_jammyjam('second') When the action list was committed resulting from the set of calls above, our user's application would not start, because the discriminators of the actions generated by the two calls are in direct conflict. Automatic conflict resolution cannot resolve the conflict (because no ``config.include`` is involved), and the user provided no intermediate :meth:`pyramid.config.Configurator.commit` call between the calls to ``add_jammyjam`` to ensure that the successive calls did not conflict with each other. This demonstrates the purpose of the discriminator argument to the action method: it's used to indicate a uniqueness constraint for an action. Two actions with the same discriminator will conflict unless the conflict is automatically or manually resolved. A discriminator can be any hashable object, but it is generally a string or a tuple. *You use a discriminator to declaratively ensure that the user doesn't provide ambiguous configuration statements.* But let's imagine that a consumer of ``add_jammyjam`` used it in such a way that no configuration conflicts are generated. .. code-block:: python config.add_jammyjam('first') What happens now? When the ``add_jammyjam`` method is called, an action is appended to the pending actions list. When the pending configuration actions are processed during :meth:`~pyramid.config.Configurator.commit`, and no conflicts occur, the *callable* provided as the second argument to the :meth:`~pyramid.config.Configurator.action` method within ``add_jammyjam`` is called with no arguments. The callable in ``add_jammyjam`` is the ``register`` closure function. It simply sets the value ``config.registry.jammyjam`` to whatever the user passed in as the ``jammyjam`` argument to the ``add_jammyjam`` function. Therefore, the result of the user's call to our directive will set the ``jammyjam`` attribute of the registry to the string ``first``. *A callable is used by a directive to defer the result of a user's call to the directive until conflict detection has had a chance to do its job*. Other arguments exist to the :meth:`~pyramid.config.Configurator.action` method, including ``args``, ``kw``, ``order``, and ``introspectables``. ``args`` and ``kw`` exist as values, which if passed will be used as arguments to the ``callable`` function when it is called back. For example, our directive might use them like so: .. code-block:: python :linenos: def add_jammyjam(config, jammyjam): def register(*arg, **kw): config.registry.jammyjam_args = arg config.registry.jammyjam_kw = kw config.registry.jammyjam = jammyjam config.action('jammyjam', register, args=('one',), kw={'two':'two'}) In the above example, when this directive is used to generate an action, and that action is committed, ``config.registry.jammyjam_args`` will be set to ``('one',)`` and ``config.registry.jammyjam_kw`` will be set to ``{'two':'two'}``. ``args`` and ``kw`` are honestly not very useful when your ``callable`` is a closure function, because you already usually have access to every local in the directive without needing them to be passed back. They can be useful, however, if you don't use a closure as a callable. ``order`` is a crude order control mechanism. ``order`` defaults to the integer ``0``; it can be set to any other integer. All actions that share an order will be called before other actions that share a higher order. This makes it possible to write a directive with callable logic that relies on the execution of the callable of another directive being done first. For example, Pyramid's :meth:`pyramid.config.Configurator.add_view` directive registers an action with a higher order than the :meth:`pyramid.config.Configurator.add_route` method. Due to this, the ``add_view`` method's callable can assume that, if a ``route_name`` was passed to it, that a route by this name was already registered by ``add_route``, and if such a route has not already been registered, it's a configuration error (a view that names a nonexistent route via its ``route_name`` parameter will never be called). .. versionchanged:: 1.6 As of Pyramid 1.6 it is possible for one action to invoke another. See :ref:`ordering_actions` for more information. Finally, ``introspectables`` is a sequence of :term:`introspectable` objects. You can pass a sequence of introspectables to the :meth:`~pyramid.config.Configurator.action` method, which allows you to augment Pyramid's configuration introspection system. .. _ordering_actions: Ordering Actions ---------------- In Pyramid every :term:`action` has an inherent ordering relative to other actions. The logic within actions is deferred until a call to :meth:`pyramid.config.Configurator.commit` (which is automatically invoked by :meth:`pyramid.config.Configurator.make_wsgi_app`). This means you may call ``config.add_view(route_name='foo')`` **before** ``config.add_route('foo', '/foo')`` because nothing actually happens until commit-time. During a commit cycle, conflicts are resolved, and actions are ordered and executed. By default, almost every action in Pyramid has an ``order`` of :const:`pyramid.config.PHASE3_CONFIG`. Every action within the same order-level will be executed in the order it was called. This means that if an action must be reliably executed before or after another action, the ``order`` must be defined explicitly to make this work. For example, views are dependent on routes being defined. Thus the action created by :meth:`pyramid.config.Configurator.add_route` has an ``order`` of :const:`pyramid.config.PHASE2_CONFIG`. Pre-defined Phases ~~~~~~~~~~~~~~~~~~ :const:`pyramid.config.PHASE0_CONFIG` - This phase is reserved for developers who want to execute actions prior to Pyramid's core directives. :const:`pyramid.config.PHASE1_CONFIG` - :meth:`pyramid.config.Configurator.add_accept_view_order` - :meth:`pyramid.config.Configurator.add_renderer` - :meth:`pyramid.config.Configurator.add_route_predicate` - :meth:`pyramid.config.Configurator.add_subscriber_predicate` - :meth:`pyramid.config.Configurator.add_view_deriver` - :meth:`pyramid.config.Configurator.add_view_predicate` - :meth:`pyramid.config.Configurator.override_asset` - :meth:`pyramid.config.Configurator.set_authorization_policy` - :meth:`pyramid.config.Configurator.set_default_csrf_options` - :meth:`pyramid.config.Configurator.set_default_permission` - :meth:`pyramid.config.Configurator.set_view_mapper` :const:`pyramid.config.PHASE2_CONFIG` - :meth:`pyramid.config.Configurator.add_route` - :meth:`pyramid.config.Configurator.set_authentication_policy` - :meth:`pyramid.config.Configurator.set_security_policy` :const:`pyramid.config.PHASE3_CONFIG` - The default for all builtin or custom directives unless otherwise specified. Calling Actions from Actions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.6 Pyramid's configurator allows actions to be added during a commit-cycle as long as they are added to the current or a later ``order`` phase. This means that your custom action can defer decisions until commit-time and then do things like invoke :meth:`pyramid.config.Configurator.add_route`. It can also provide better conflict detection if your addon needs to call more than one other action. For example, let's make an addon that invokes ``add_route`` and ``add_view``, but we want it to conflict with any other call to our addon: .. code-block:: python :linenos: from pyramid.config import PHASE0_CONFIG def includeme(config): config.add_directive('add_auto_route', add_auto_route) def add_auto_route(config, name, view): def register(): config.add_view(route_name=name, view=view) config.add_route(name, '/' + name) config.action(('auto route', name), register, order=PHASE0_CONFIG) Now someone else can use your addon and be informed if there is a conflict between this route and another, or two calls to ``add_auto_route``. Notice how we had to invoke our action **before** ``add_view`` or ``add_route``. If we tried to invoke this afterward, the subsequent calls to ``add_view`` and ``add_route`` would cause conflicts because that phase had already been executed, and the configurator cannot go back in time to add more views during that commit-cycle. .. code-block:: python :linenos: from pyramid.config import Configurator def main(global_config, **settings): config = Configurator() config.include('auto_route_addon') config.add_auto_route('foo', my_view) def my_view(request): return request.response .. _introspection: Adding Configuration Introspection ---------------------------------- .. versionadded:: 1.3 Pyramid provides a configuration introspection system that can be used by debugging tools to provide visibility into the configuration of a running application. All built-in Pyramid directives (such as :meth:`pyramid.config.Configurator.add_view` and :meth:`pyramid.config.Configurator.add_route`) register a set of introspectables when called. For example, when you register a view via ``add_view``, the directive registers at least one introspectable: an introspectable about the view registration itself, providing human-consumable values for the arguments passed into it. You can later use the introspection query system to determine whether a particular view uses a renderer, or whether a particular view is limited to a particular request method, or against which routes a particular view is registered. The Pyramid "debug toolbar" makes use of the introspection system in various ways to display information to Pyramid developers. Introspection values are set when a sequence of :term:`introspectable` objects is passed to the :meth:`~pyramid.config.Configurator.action` method. Here's an example of a directive which uses introspectables: .. code-block:: python :linenos: def add_jammyjam(config, value): def register(): config.registry.jammyjam = value intr = config.introspectable(category_name='jammyjams', discriminator='jammyjam', title='a jammyjam', type_name=None) intr['value'] = value config.action('jammyjam', register, introspectables=(intr,)) if __name__ == '__main__': config = Configurator() config.add_directive('add_jammyjam', add_jammyjam) If you notice, the above directive uses the ``introspectable`` attribute of a Configurator (:attr:`pyramid.config.Configurator.introspectable`) to create an introspectable object. The introspectable object's constructor requires at least four arguments: the ``category_name``, the ``discriminator``, the ``title``, and the ``type_name``. The ``category_name`` is a string representing the logical category for this introspectable. Usually the category_name is a pluralization of the type of object being added via the action. The ``discriminator`` is a value unique **within the category** (unlike the action discriminator, which must be unique within the entire set of actions). It is typically a string or tuple representing the values unique to this introspectable within the category. It is used to generate links and as part of a relationship-forming target for other introspectables. The ``title`` is a human-consumable string that can be used by introspection system frontends to show a friendly summary of this introspectable. The ``type_name`` is a value that can be used to subtype this introspectable within its category for sorting and presentation purposes. It can be any value. An introspectable is also dictionary-like. It can contain any set of key/value pairs, typically related to the arguments passed to its related directive. While the ``category_name``, ``discriminator``, ``title``, and ``type_name`` are *metadata* about the introspectable, the values provided as key/value pairs are the actual data provided by the introspectable. In the above example, we set the ``value`` key to the value of the ``value`` argument passed to the directive. Our directive above mutates the introspectable, and passes it in to the ``action`` method as the first element of a tuple as the value of the ``introspectable`` keyword argument. This associates this introspectable with the action. Introspection tools will then display this introspectable in their index. Introspectable Relationships ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Two introspectables may have relationships between each other. .. code-block:: python :linenos: def add_jammyjam(config, value, template): def register(): config.registry.jammyjam = (value, template) intr = config.introspectable(category_name='jammyjams', discriminator='jammyjam', title='a jammyjam', type_name=None) intr['value'] = value tmpl_intr = config.introspectable(category_name='jammyjam templates', discriminator=template, title=template, type_name=None) tmpl_intr['value'] = template intr.relate('jammyjam templates', template) config.action('jammyjam', register, introspectables=(intr, tmpl_intr)) if __name__ == '__main__': config = Configurator() config.add_directive('add_jammyjam', add_jammyjam) In the above example, the ``add_jammyjam`` directive registers two introspectables: the first is related to the ``value`` passed to the directive, and the second is related to the ``template`` passed to the directive. If you believe a concept within a directive is important enough to have its own introspectable, you can cause the same directive to register more than one introspectable, registering one introspectable for the "main idea" and another for a related concept. The call to ``intr.relate`` above (:meth:`pyramid.interfaces.IIntrospectable.relate`) is passed two arguments: a category name and a directive. The example above effectively indicates that the directive wishes to form a relationship between the ``intr`` introspectable and the ``tmpl_intr`` introspectable; the arguments passed to ``relate`` are the category name and discriminator of the ``tmpl_intr`` introspectable. Relationships need not be made between two introspectables created by the same directive. Instead a relationship can be formed between an introspectable created in one directive and another introspectable created in another by calling ``relate`` on either side with the other directive's category name and discriminator. An error will be raised at configuration commit time if you attempt to relate an introspectable with another nonexistent introspectable, however. Introspectable relationships will show up in frontend system renderings of introspection values. For example, if a view registration names a route name, the introspectable related to the view callable will show a reference to the route to which it relates and vice versa.