Is there a built-in product() in Python? [duplicate]

Question

I've been looking through a tutorial and book but I can find no mention of a built in product function i.e. of the same type as sum(), but I could not find anything such as prod().

Is the only way I could find the product of items in a list by importing the mul() operator?

Answer 1

Pronouncement

Yes, that's right. Guido rejected the idea for a built-in prod() function because he thought it was rarely needed.

Python 3.8 Update

In Python 3.8, prod() was added to the math module:

>>> from math import prod >>> prod(range(1, 11)) 3628800 

Alternative with reduce()

As you suggested, it is not hard to make your own using reduce() and operator.mul():

def prod(iterable):     return reduce(operator.mul, iterable, 1)  >>> prod(range(1, 5)) 24 

In Python 3, the reduce() function was moved to the functools module, so you would need to add:

from functools import reduce 

Specific case: Factorials

As a side note, the primary motivating use case for prod() is to compute factorials. We already have support for that in the math module:

>>> import math  >>> math.factorial(10) 3628800 

Alternative with logarithms

If your data consists of floats, you can compute a product using sum() with exponents and logarithms:

>>> from math import log, exp  >>> data = [1.2, 1.5, 2.5, 0.9, 14.2, 3.8] >>> exp(sum(map(log, data))) 218.53799999999993  >>> 1.2 * 1.5 * 2.5 * 0.9 * 14.2 * 3.8 218.53799999999998 

Answer 2

There is no product in Python, but you can define it as

def product(iterable):     return reduce(operator.mul, iterable, 1) 

Or, if you have NumPy, use numpy.product.