import weakref

class Event(object):

# a basic event class

def __init__(self, name, payload=None):

self.name = name

self.payload = payload

class EventHandler(object):

# This partial base class provides the framework to handle events.

def initialize_event_handling(self):

self.event_handlers = {}

def add_event_hander(self, event_name, handler):

if not event_name in self.event_handlers:

self.event_handlers[event_name] = set() # weakref.WeakSet() #Why doesn't the WeakSet work?

self.event_handlers[event_name].add(handler)

parent_app = self.find_parent_app()

if parent_app:

parent_app.register_for_event(self, event_name)

else:

# Probably are the parent App!

# but could be a form outside a proper application environment

try:

self.register_for_event(self, event_name)

except AttributeError:

pass

def remove_event_handler(self, event_name, handler):

if event_name in self.event_handlers:

self.event_handlers[event_name].remove(handler)

if not self.event_handlers[event_name]:

self.event_handlers.pop({})

def handle_event(self, event):

"return True if the event was handled. Return False if the application should stop sending this event."

if event.name not in self.event_handlers:

return False

else:

remove_list = []

for handler in self.event_handlers[event.name]:

try:

handler(event)

except weakref.ReferenceError:

remove_list.append(handler)

for dead_handler in remove_list:

self.event_handlers[event.name].remove(handler)

return True

def find_parent_app(self):

if hasattr(self, "parentApp"):

return self.parentApp

elif hasattr(self, "parent") and hasattr(self.parent, "parentApp"):

return self.parent.parentApp

else:

return None