Question

How do I find the arithmetic mean of a list in Python? For example:

[1, 2, 3, 4]  ⟶  2.5

Answer 1

For Python 3.8+, use statistics.fmean for numerical stability with floats. (Fast.)

For Python 3.4+, use statistics.mean for numerical stability with floats. (Slower.)

xs = [15, 18, 2, 36, 12, 78, 5, 6, 9]

import statistics
statistics.mean(xs)  # = 20.11111111111111

For older versions of Python 3, use

sum(xs) / len(xs)

For Python 2, convert len to a float to get float division:

sum(xs) / float(len(xs))