standard deviation of the values

std.py

from math import sqrt

sum, sum2, n = 0.0, 0.0, 0.0
with open("numeros.txt") as infile:
    for line in infile:
        k = float(line)
        sum += k
        sum2 += k*k
        n += 1

print sqrt(sum2/n - (sum/n)**2)