Using __mul__

Sam Jervis sam at heffalump.me.uk
Sat Jul 3 16:38:24 CEST 2004


Thomas Philips wrote:
> To compute the product of a list of numbers, I tried entering
> 
>>>>reduce(__mul__,[1,2,3])
> 
> 
> Traceback (most recent call last):
>   File "<pyshell#0>", line 1, in -toplevel-
>     reduce(__mul__,[1,2,3])
> NameError: name '__mul__' is not defined
> 
> I can get the answer I want by defining a function that returns the
> product of two numbers:
> 
>>>>def product(x,y):
> 
> 	return x*y
> 
> and then using it:
> 
>>>>reduce(product,[1,2,3])
> 
> 6
> 
> But why does my first approach not work? __mul__ is a valid method of
> type int. Is there an obvious flaw in my logic?
> 
> Thomas Philips

The answer is in your question.  __mul__ is a valid method of type int, 
but __mul__ on its own is an undefined name.  The following code works:

	reduce(int.__mul__, [1, 2, 3])

Sam



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