CHAPTER

FORTYFIVE

PYRAMID.EVENTS

45.1 Functions

subscriber(*ifaces)

Decorator activated via a scan which treats the function being decorated as an event subscriber for the set of interfaces passed as *ifaces to the decorator constructor.

For example:

from pyramid.events import NewRequest from pyramid.events import subscriber

@subscriber(NewRequest) def mysubscriber(event):

event.request.foo = 1

More than one event type can be passed as a constructor argument. The decorated subscriber will be called for each event type.

from pyramid.events import NewRequest, NewResponse from pyramid.events import subscriber

@subscriber(NewRequest, NewResponse) def mysubscriber(event):

print event

When the subscriber decorator is used without passing an arguments, the function it decorates is called for every event sent:

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from pyramid.events import subscriber

@subscriber()

def mysubscriber(event): print event

This method will have no effect until a scan is performed against the package or module which contains it, ala:

from pyramid.config import Configurator config = Configurator()

config.scan(’somepackage_containing_subscribers’)

45.2 Event Types

class ApplicationCreated(app)

An instance of this class is emitted as an event when the pyramid.config.Configurator.make_wsgi_app() is called. The instance has an attribute, app, which is an instance of the router that will handle WSGI requests. This class implements the pyramid.interfaces.IApplicationCreated interface.

latex-note.png

For backwards compatibility purposes, this class can also be imported as pyramid.events.WSGIApplicationCreatedEvent. This was the name of the event class before Pyramid 1.0.

class NewRequest(request)

An instance of this class is emitted as an event whenever Pyramid begins to process a new request. The event instance has an attribute, request, which is a request object. This event class implements the pyramid.interfaces.INewRequest interface.

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45.2. EVENT TYPES

class ContextFound(request)

An instance of this class is emitted as an event after the Pyramid router finds a context object (after it performs traversal) but before any view code is executed. The instance has an attribute, request, which is the request object generated by Pyramid.

Notably, the request object will have an attribute named context, which is the context that will be provided to the view which will eventually be called, as well as other attributes attached by context-finding code.

This class implements the pyramid.interfaces.IContextFound interface.

latex-note.png

As of Pyramid 1.0, for backwards compatibility purposes, this event may also be imported as pyramid.events.AfterTraversal.

class NewResponse(request, response)

An instance of this class is emitted as an event whenever any Pyramid view or exception view returns a response.

The instance has two attributes:request, which is the request which caused the response, and response, which is the response object returned by a view or renderer.

If the response was generated by an exception view, the request will have an attribute named exception, which is the exception object which caused the exception view to be executed. If the response was generated by a ‘normal’ view, this attribute of the request will be None.

This event will not be generated if a response cannot be created due to an exception that is not caught by an exception view (no response is created under this circumstace).

This class implements the pyramid.interfaces.INewResponse interface.

latex-note.png
				Postprocessing a response is usually better	han-
dled	in a	WSGI		middleware component than in subscriber code	that
is	called	by a		pyramid.interfaces.INewResponse event.	The

pyramid.interfaces.INewResponse event exists almost purely for symmetry with the pyramid.interfaces.INewRequest event.

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class BeforeRender(system, rendering_val=None)

Subscribers to this event may introspect and modify the set of renderer globals before they are passed to a renderer. This event object iself has a dictionary-like interface that can be used for this purpose. For example:

from pyramid.events import subscriber from pyramid.events import BeforeRender

@subscriber(BeforeRender) def add_global(event):

event[’mykey’] = ’foo’

An object of this type is sent as an event just before a renderer is invoked (but after the – deprecated – application-level renderer globals factory added via

pyramid.config.Configurator.set_renderer_globals_factory,	if any,
has injected its own keys into the renderer globals dictionary).

If a subscriber adds a key via __setitem__ that already exists in the renderer globals dictionary, it will overwrite the older value there. This can be problematic because event subscribers to the BeforeRender event do not possess any relative ordering. For maximum interoperability with other third-party subscribers, if you write an event subscriber meant to be used as a BeforeRender subscriber, your subscriber code will need to ensure no value already exists in the renderer globals dictionary before setting an overriding value (which can be done using .get or __contains__ of the event object).

The event has an additional attribute named rendering_val. This is the (non-system) value returned by a view or passed to render* as value. This feature is new in Pyramid 1.2.

For a description of the values present in the renderer globals dictionary, see System Values Used During Rendering.

See also pyramid.interfaces.IBeforeRender.

update(E, **F)

Update D from dict/iterable E and F. If E has a .keys() method, does: for k in E: D[k] = E[k] If E lacks .keys() method, does: for (k, v) in E: D[k] = v. In either case, this is followed by: for k in F: D[k] = F[k].

clear() ! None. Remove all items from D.

copy() ! a shallow copy of D

static fromkeys(S[, v ]) ! New dict with keys from S and values equal to v. v defaults to None.

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45.2. EVENT TYPES

get(k[, d ]) ! D[k] if k in D, else d. d defaults to None.

has_key(k) ! True if D has a key k, else False

items() ! list of D’s (key, value) pairs, as 2-tuples

iteritems() ! an iterator over the (key, value) items of D

iterkeys() ! an iterator over the keys of D

itervalues() ! an iterator over the values of D

keys() ! list of D’s keys

pop(k[, d ]) ! v, remove specified key and return the corresponding value. If key is not found, d is returned if given, otherwise KeyError is raised

popitem() ! (k, v), remove and return some (key, value) pair as a 2-tuple; but raise KeyError if D is empty.

setdefault(k[, d ]) ! D.get(k,d), also set D[k]=d if k not in D

values() ! list of D’s values

viewitems() ! a set-like object providing a view on D’s items

viewkeys() ! a set-like object providing a view on D’s keys

viewvalues() ! an object providing a view on D’s values

See Using Events for more information about how to register code which subscribes to these events.

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