pydispatch.dispatch module

Dispatcher class

class Dispatcher(*args, **kwargs)

Core class used to enable all functionality in the library

Interfaces with Event and Property objects upon instance creation.

Events can be created by calling register_event() or by the subclass definition:

class Foo(Dispatcher):
    _events_ = ['awesome_event', 'on_less_awesome_event']

Once defined, an event can be dispatched to listeners by calling emit().

bind(**kwargs)

Subscribes to events or to Property updates

Keyword arguments are used with the Event or Property names as keys and the callbacks as values:

class Foo(Dispatcher):
    name = Property()

foo = Foo()

foo.bind(name=my_listener.on_foo_name_changed)
foo.bind(name=other_listener.on_name,
         value=other_listener.on_value)

The callbacks are stored as weak references and their order is not maintained relative to the order of binding.

Async Callbacks:

Callbacks may be coroutine functions (defined using async def or decorated with @asyncio.coroutine), but an event loop must be explicitly provided with the keyword argument "__aio_loop__" (an instance of asyncio.BaseEventLoop):

import asyncio
from pydispatch import Dispatcher

class Foo(Dispatcher):
    _events_ = ['test_event']

class Bar(object):
    def __init__(self):
        self.got_foo_event = asyncio.Event()
    async def wait_for_foo(self):
        await self.got_foo_event.wait()
        print('got foo!')
    async def on_foo_test_event(self, *args, **kwargs):
        self.got_foo_event.set()

foo = Foo()
bar = Bar()

loop = asyncio.get_event_loop()
foo.bind(test_event=bar.on_foo_test_event, __aio_loop__=loop)

loop.run_until_complete(bar.wait_for_foo())

This can also be done using bind_async().

New in version 0.1.0.

bind_async(loop, **kwargs)

Subscribes to events with async callbacks

Functionality is matches the bind() method, except the provided callbacks should be coroutine functions. When the event is dispatched, callbacks will be placed on the given event loop.

For keyword arguments, see bind().

Parameters:loop – The EventLoop to use when events are dispatched

Availability:

Python>=3.5

New in version 0.1.0.

emission_lock(name)

Holds emission of events and dispatches the last event on release

The context manager returned will store the last event data called by emit() and prevent callbacks until it exits. On exit, it will dispatch the last event captured (if any):

class Foo(Dispatcher):
    _events_ = ['my_event']

def on_my_event(value):
    print(value)

foo = Foo()
foo.bind(my_event=on_my_event)

with foo.emission_lock('my_event'):
    foo.emit('my_event', 1)
    foo.emit('my_event', 2)

>>> 2

Parameters:name (str) – The name of the Event or Property Returns:A context manager to be used by the with statement.

If available, this will also be an async context manager to be used with the async with statement (see PEP 492).

Note

The context manager is re-entrant, meaning that multiple calls to this method within nested context scopes are possible.

emit(name, *args, **kwargs)

Dispatches an event to any subscribed listeners

Note

If a listener returns False, the event will stop dispatching to other listeners. Any other return value is ignored.

Parameters:

• name (str) – The name of the Event to dispatch
• *args (Optional) – Positional arguments to be sent to listeners
• **kwargs (Optional) – Keyword arguments to be sent to listeners

get_dispatcher_event(name)

Retrieves an Event object by name

Parameters:name (str) – The name of the Event or Property object to retrieve Returns:The Event instance for the event or property definition

New in version 0.1.0.

register_event(*names)

Registers new events after instance creation

Parameters:*names (str) – Name or names of the events to register

unbind(*args)

Unsubscribes from events or Property updates

Multiple arguments can be given. Each of which can be either the method that was used for the original call to bind() or an instance object.

If an instance of an object is supplied, any previously bound Events and Properties will be ‘unbound’.

Event class

class Event(name)

Holds references to event names and subscribed listeners

This is used internally by Dispatcher.

__call__(*args, **kwargs)

Dispatches the event to listeners

Called by emit()