The following example code creates a Sender class (named Alice). Sender keeps track of interested listeners and notifies them accordingly. In more detail, this is achieved by a dictionary containing a function-event mapping, Sender.listeners.
A listener class can be of any type, here I make a bunch of ExampleListener classes, named Bob,Dave & Charlie. All of them have a method, that is that is subscribed to Sender. The only special thing about the subscribed method is that it should contain three parameters: sender, event, message. Sender is the class reference of the Sender class, so a listener would know who sent the message. Event is an identifier, for which I usually use a string. Optionally, a message is the data that is passed to a function.
A nice detail is that if a listener method throws an exception, it is automatically unsubscribed from further events.
'''
Created on 26 dec. 2011
Copyright: Jev Kuznetsov
License: BSD
sender-reciever pattern.
'''
import tradingWithPython.lib.logger as logger
import types
class Sender(object):
"""
Sender -> dispatches messages to interested callables
"""
def __init__(self):
self.listeners = {}
self.logger = logger.getLogger()
def register(self,listener,events=None):
"""
register a listener function
Parameters
-----------
listener : external listener function
events : tuple or list of relevant events (default=None)
"""
if events is not None and type(events) not in (types.TupleType,types.ListType):
events = (events,)
self.listeners[listener] = events
def dispatch(self,event=None, msg=None):
"""notify listeners """
for listener,events in self.listeners.items():
if events is None or event is None or event in events:
try:
listener(self,event,msg)
except (Exception,):
self.unregister(listener)
errmsg = "Exception in message dispatch: Handler '{0}' unregistered for event '{1}' ".format(listener.func_name,event)
self.logger.exception(errmsg)
def unregister(self,listener):
""" unregister listener function """
del self.listeners[listener]
#---------------test functions--------------
class ExampleListener(object):
def __init__(self,name=None):
self.name = name
def method(self,sender,event,msg=None):
print "[{0}] got event {1} with message {2}".format(self.name,event,msg)
if __name__=="__main__":
print 'demonstrating event system'
alice = Sender()
bob = ExampleListener('bob')
charlie = ExampleListener('charlie')
dave = ExampleListener('dave')
# add subscribers to messages from alice
alice.register(bob.method,events='event1') # listen to 'event1'
alice.register(charlie.method,events ='event2') # listen to 'event2'
alice.register(dave.method) # listen to all events
# dispatch some events
alice.dispatch(event='event1')
alice.dispatch(event='event2',msg=[1,2,3])
alice.dispatch(msg='attention to all')
print 'Done.'
