compute mean in python for a generator

Question

I'm doing some statistics work, I have a (large) collection of random numbers to compute the mean of, I'd like to work with generators, because I just need to compute the mean, so I don't need to store the numbers.

The problem is that numpy.mean breaks if you pass it a generator. I can write a simple function to do what I want, but I'm wondering if there's a proper, built-in way to do this?

It would be nice if I could say "sum(values)/len(values)", but len doesn't work for genetators, and sum already consumed values.

here's an example:

import numpy 

def my_mean(values):
    n = 0
    Sum = 0.0
    try:
        while True:
            Sum += next(values)
            n += 1
    except StopIteration: pass
    return float(Sum)/n

X = [k for k in range(1,7)]
Y = (k for k in range(1,7))

print numpy.mean(X)
print my_mean(Y)

these both give the same, correct, answer, buy my_mean doesn't work for lists, and numpy.mean doesn't work for generators.

I really like the idea of working with generators, but details like this seem to spoil things.

Answer 1

Just one simple change to your code would let you use both. Generators were meant to be used interchangeably to lists in a for-loop.

def my_mean(values):
    n = 0
    Sum = 0.0
    for v in values:
        Sum += v
        n += 1
    return Sum / n