Using __mul__

[Thomas Philips]

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: 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

 

[Sam Jervis]

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:

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

 

[Peter Otten]

To compute the product of a list of numbers, I tried entering

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

[...]

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])

Or use operator.mul if you cannot guarantee that all numbers are integers:

reduce(int.__mul__, [1.0, 2, 3])

Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: descriptor '__mul__' requires a 'int' object but received a
'float'

reduce(operator.mul, [1.0, 2, 3])

6.0

Peter