hooks.py

from threading import RLock
import traceback, inspect
               
class BadArgLength(AttributeError): pass               

class Subscriber(object):
    def __init__(self, func, subscriberargs):
        self.func = func
        self.args = subscriberargs
        
    def fire(self, args):
        allargs = args + self.args
        self.func(*allargs)
        
    __call__ = fire
               
class Hook(object):
    def __init__(self, numargs, doc=None):
        self._numargs = numargs
        
        if doc:
            self.__doc__ = doc
            
        self.subscribers = list()
        self._lock = RLock()
        
    def attach(self, func, *customargs):
        if callable(func):
            # Lets make sure that the function's signature has the 
            # right amount of arguments!
            arglength = len(inspect.getargspec(func).args)
            reqlength = self._numargs + len(customargs)
            
            if reqlength == arglength:
                s = Subscriber(func, customargs)
                
                with self._lock:
                    self.subscribers.append(s)
                    
                return s
            
            # Incorrect number of arguments!
            raise BadArgLength(
                "%s needs to support %d native and %d custom args, but has %d!" % 
                (func, self._numargs, len(customargs), arglength))
            
        # Purposely raise an error, as at this point, it's not callable.
        raise TypeError("%s is not callable!" % func)

    def detach(self, func):
        with self._lock:
            for subscriber in self.subscribers:
                if subscriber.func == func:
                    self.subscribers.remove(subscriber)

    def fire(self, *args):
        with self._lock:
            subscribers = self.subscribers[:]
            
        for subscriber in subscribers:
            try:
                subscriber(args)
                    
            except Exception:
                print "----- Exception! -----"
                traceback.print_exc(5)
                print "----------------------"
                    
    __call__ = fire