Is there a built-in product() in Python? [duplicate]
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 * 3.8218.53799999999998
Since the reduce() function has been moved to the module functools
python 3.0, you have to take a different approach.
You can use functools.reduce()
to access the function:
product = functools.reduce(operator.mul, iterable, 1)
Or, if you want to follow the spirit of the python-team (which removed reduce()
because they think for
would be more readable), do it with a loop:
product = 1for x in iterable: product *= x