A event implementation like boost::signal or C# event.

event.py

class AggregateException(Exception):
    def __init__(self, *args, **kwargs):
        super(self.__class__, self).__init__(*args, **kwargs)
        self.sub_exceptions = []

    def add(self, exception):
        self.sub_exceptions.append(exception)

    @property
    def message(self):
        return '\n'.join([e.message for e in self.sub_exceptions])

    def __nonzero__(self):
        return bool(self.sub_exceptions)


class Event(object):
    def __init__(self, *param_type_list, **kwargs):
        'param_type_list is optional, elide to disable parameter types check.'

        self.callbacks = []
        self.param_type_list = param_type_list
        self.continue_on_exception = kwargs.get('continue_on_exception', False)

    def __call__(self, *args, **kwargs):
        'Check then call.'

        if self.param_type_list:
            for i, a in enumerate(args, start=1):
                t = self.param_type_list[i - 1]
                if not isinstance(a, t):
                    raise ValueError('Error parameter type at %d, '
                                     'value %s, should be %s.' % (i, a, t))

        exception_set = AggregateException()
        for c in self.callbacks:
            try:
                c(*args, **kwargs)
            except Exception as e:
                if not self.continue_on_exception:
                    raise
                exception_set.add(e)

        if exception_set:
            raise exception_set

    def add(self, callback):
        self.callbacks.append(callback)

    def remove(self, callback):
        self.callbacks.remove(callback)
# <-- Line 52 Here. Sorry, Sam.


def ____________________________():
    print '-' * 32


def test():
    def say_hi(name, greeting_msg):
        print 'Hi, %s.' % name

    def echo(name, greeting_msg):
        print '%s said, %s.' % (name, greeting_msg)

    def bad_func(name, greeting_msg):
        raise Exception('I am bad.')

    on_greeting = Event(str, str)

    on_greeting.add(say_hi)
    on_greeting.add(echo)

    on_greeting('Logan', 'Hello')

    ____________________________()

    on_greeting = Event(str, str, continue_on_exception=True)

    on_greeting.add(say_hi)
    on_greeting.add(bad_func)
    on_greeting.add(echo)

    on_greeting('Sam', 'Hi')

test()