functors

[Tom Plunket]

How can I create a functor object in Python?

What I want (being a C++ coder <g>), is to be able to create an
object that I is callable.  The following is my attempt, but it
doesn't work:

class Countdown:
    def __init__(self):
        self.callback = None

    def SetCallback(self, time, callback):
        self.callback = callback
        self.timeRemaining = time
        
    def Update(self):
        if self.callback is not None:
            self.timeRemaining -= 1
            if self.timeRemaining <= 0:
                print "Callback fired."
                self.callback()
                self.callback = None
                
class SomeClass:
    def __init__(self):
        self.countdown = Countdown()
        self.countdown.SetCallback(30, lambda s=self: s.Callback)
        # I have also tried 'lambda: self.Callback'
        self.done = False

    def Callback(self):
        print "success!"
        self.done = True
        
    def Update(self):
        while not self.done:
            self.countdown.Update()

if __name__ == "__main__":
    SomeClass().Update()

***

I wouldn't mind creating a new class to wrap this up (that's what
I'd do in C++, and that class would have an operator() defined),
but I can't seem to discover how to make callable objects in
Python.

If there's a better way to do callbacks like I'm trying to do,
also that would be handy to know.  :)  I don't want to poll the
countdown object every time through the loop because it just
seems "dirty"...  :)

thanks,
-tom!