functors

[Bruno Desthuilliers]

Tom Plunket wrote:
> 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. 

__call__ is your friend.

> 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)

This is not the same problem as making an object (ie a class instance) 
callable. Here you just want to use an instance object as callback function.

Functions in Python are first-class objects, so you don't need this 
lambda stuff. This should work (I tried a simplified version...):

          self.countdown.SetCallback(30, self.Callback)


HTH
Bruno