Event Systems - Existing and Implementation

[lrh9]

I'm interested in a generic event system for Python. I've searched the forum for similar topics, and I've searched the web for existing implementations. I haven't found exactly what I'm looking for.

I'm familiar with the Observer pattern. However, my implementation and other implementations lack strong support for concurrency and scheduling.

Do you know of anything that fits the bill or can you help me create an implementation?

I want to use this for simulations and games.

[Gribouillis]

I know a very simple system called py-notify. See here http://home.gna.org/py-notify. It define 'signals' emitted by your code, which can be 'connected' to callback functions.

[lrh9]

I've downloaded it, and I'm attempting to understand the source.

I wrote my own naive event loop, but I'm getting a maximum recursion depth exceeded RuntimeError.

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import collections
import heapq
import random
import time

__all__ = ['InstantNotification',
           'Notification',
           'InstantMessage',
           'Message'
           'Dispatcher']

class InstantNotification:

    __slots__ = ('type', 'sender', 'receivers')

    def __init__(self,
                 type,
                 sender=None,
                 receivers=None):
        self.type = type
        self.sender = sender
        self.receivers = receivers

class Notification(InstantNotification):

    __slots__ = ('delay')

    def __lt__(self, other):
        return self.delay < other.delay

class InstantMessage(InstantNotification):

    __slots__ = ('data')

    def __init__(self,
                 type,
                 data,
                 sender=None,
                 receivers=None):
        self.data = data
        super().__init__(type, sender, receivers)

class Message(InstantMessage):

    __slots__ = ('delay')

    def __lt__(self, other):
        return self.delay < other.delay

class Dispatcher:

    __slots__ = ('types', 'items')

    def __init__(self):
        self.types = collections.defaultdict(dict)
        self.items = list()

    def receive(self, item, delay):
        item.delay = delay
        heapq.heappush(self.items, item)

    def deliver(self, item):
        potential_receivers = self.types[item.type]
        receivers = item.receivers
        if receivers:
            for receiver in receivers:
                potential_receivers[receiver](item)
        else:
            for receiver in potential_receivers.values():
                receiver(item)

    def register(self, type, receiver, callback):
        self.types[type][receiver] = callback

    def unregister(self, type, key):
        del self.types[type][receiver]

    def update(self, decrement):
        while True:
            item = heapqueue.heappop(self.items)
            item.delay -= decrement
            if item.delay <= 0:
                self.dispatch(item)
            else:
                for item in self.items:
                    item.delay -= decrement
                break

if __name__ == '__main__':

    DISPATCHER = Dispatcher()

    class LightSwitch:

        def __init__(self):
            self.state = True
            self.switch()

        def switch(self):
            self.state = not self.state
            DISPATCHER.deliver(InstantMessage(LightSwitch, {'state': self.state}, self))

    class Waster:

        def __init__(self):
            DISPATCHER.register(LightSwitch, self, self.on_LightSwitch)

        #These make recursion errors!
        def on_LightSwitch(self, message):
            if not message.data['state']:
                if not message.sender.state:
                    print('Shiny lights are on at {t}!'.format(t=time.clock()))
                    message.sender.switch()

    class Saver:

        def __init__(self):
            DISPATCHER.register(LightSwitch, self, self.on_LightSwitch)

        def on_LightSwitch(self, message):
            if message.data['state']:
                if message.sender.state:
                    print("Keep those dang lights out! It's {t}!".format(t=time.clock()))
                    message.sender.switch()

    waster = Waster()
    saver = Saver()
    light_switch = LightSwitch()

[predator78]

What module is generating the error? Once you know that then you know to change that module to not be recursive if it is exceeding the limit.

[lrh9]

The one I wrote. I'd have to take the time to discern the pattern in the traceback or limit the recursion limit. Otherwise there are just too many lines in the traceback.

[predator78]

Indeed you will have to trace it back because it's not generating it in that module.

[lrh9]

I ended up checking out Panda3D's task and event system. Thanks for the replies.