pydispatch.dispatcher

Multiple-producer-multiple-consumer signal-dispatching

dispatcher is the core of the PyDispatcher system, providing the primary API and the core logic for the system.

Module attributes of note:

Any: Singleton used to signal either "Any Sender" or "Any Signal". See documentation of the _Any class.
Anonymous: Singleton used to signal "Anonymous Sender" See documentation of the _Anonymous class.

Internal attributes: WEAKREF_TYPES -- tuple of types/classes which represent weak references to receivers, and thus must be de- referenced on retrieval to retrieve the callable object connections -- { senderkey (id) : { signal : senders -- { senderkey (id) : weakref(sender) } used for cleaning up sender references on sender deletion sendersBack -- { receiverkey (id) : [senderkey (id)... } used for cleaning up receiver references on receiver deletion, (considerably speeds up the cleanup process vs. the original code.)

Functions

_cleanupConnections( senderkey , signal )

Delete any empty signals for senderkey. Delete senderkey if empty.

_killBackref( receiver , senderkey )

Do the actual removal of back reference from receiver to senderkey

_removeBackrefs( senderkey )

Remove all back-references to this senderkey

_removeOldBackRefs( senderkey , signal , receiver , receivers )

Kill old sendersBack references from receiver

This guards against multiple registration of the same receiver for a given signal and sender leaking memory as old back reference records build up.

Also removes old receiver instance from receivers

_removeReceiver( receiver )

Remove receiver from connections.

_removeSender( senderkey )

Remove senderkey from connections.

connect( receiver , signal = _Any , sender = _Any , weak = True )

Connect receiver to sender for signal

receiver: a callable Python object which is to receive messages/signals/events. Receivers must be hashable objects.

if weak is True, then receiver must be weak-referencable (more precisely saferef.safeRef() must be able to create a reference to the receiver).

Receivers are fairly flexible in their specification, as the machinery in the robustApply module takes care of most of the details regarding figuring out appropriate subsets of the sent arguments to apply to a given receiver.

Note: if receiver is itself a weak reference (a callable), it will be de-referenced by the system's machinery, so *generally* weak references are not suitable as receivers, though some use might be found for the facility whereby a higher-level library passes in pre-weakrefed receiver references.

signal: the signal to which the receiver should respond

if Any, receiver will receive any signal from the indicated sender (which might also be Any, but is not necessarily Any).

Otherwise must be a hashable Python object other than None (DispatcherError raised on None).

sender: the sender to which the receiver should respond

if Any, receiver will receive the indicated signals from any sender.

if Anonymous, receiver will only receive indicated signals from send/sendExact which do not specify a sender, or specify Anonymous explicitly as the sender.

Otherwise can be any python object.

weak: whether to use weak references to the receiver By default, the module will attempt to use weak references to the receiver objects. If this parameter is false, then strong references will be used.

returns None, may raise DispatcherTypeError

disconnect( receiver , signal = _Any , sender = _Any , weak = True )

Disconnect receiver from sender for signal

receiver: the registered receiver to disconnect
signal: the registered signal to disconnect
sender: the registered sender to disconnect
weak: the weakref state to disconnect

disconnect reverses the process of connect, the semantics for the individual elements are logically equivalent to a tuple of (receiver, signal, sender, weak) used as a key to be deleted from the internal routing tables. (The actual process is slightly more complex but the semantics are basically the same).

Note: Using disconnect is not required to cleanup routing when an object is deleted, the framework will remove routes for deleted objects automatically. It's only necessary to disconnect if you want to stop routing to a live object.

returns None, may raise DispatcherTypeError or DispatcherKeyError

getAllReceivers( sender = _Any , signal = _Any )

Get list of all receivers from global tables

This gets all receivers which should receive the given signal from sender, each receiver should be produced only once by the resulting generator

getReceivers( sender = _Any , signal = _Any )

Get list of receivers from global tables

This utility function allows you to retrieve the raw list of receivers from the connections table for the given sender and signal pair.

Note: there is no guarantee that this is the actual list stored in the connections table, so the value should be treated as a simple iterable/truth value rather than, for instance a list to which you might append new records.

Normally you would use liveReceivers( getReceivers( ...)) to retrieve the actual receiver objects as an iterable object.

liveReceivers( receivers )

Filter sequence of receivers to get resolved, live receivers

This is a generator which will iterate over the passed sequence, checking for weak references and resolving them, then returning all live receivers.

send( signal = _Any , sender = _Anonymous , * arguments , ** named )

Send signal from sender to all connected receivers.

signal: hashable) signal value, see connect for details

sender: the sender of the signal

if Any, only receivers registered for Any will receive the message.

if Anonymous, only receivers registered to receive messages from Anonymous or Any will receive the message

Otherwise can be any python object (normally one registered with a connect if you actually want something to occur).

arguments: positional arguments which will be passed to *all* receivers. Note that this may raise TypeErrors if the receivers do not allow the particular arguments. Note also that arguments are applied before named arguments, so they should be used with care.

named: named arguments which will be filtered according to the parameters of the receivers to only provide those acceptable to the receiver.

Return a list of tuple pairs response), ...

if any receiver raises an error, the error propagates back through send, terminating the dispatch loop, so it is quite possible to not have all receivers called if a raises an error.

sendExact( signal = _Any , sender = _Anonymous , * arguments , ** named )

Send signal only to those receivers registered for exact message

sendExact allows for avoiding Any/Anonymous registered handlers, sending only to those receivers explicitly registered for a particular signal on a particular sender.