Wondering about http://python-karan.blogspot.co.uk/2013/07/sum-of-digits-of-number-in-one-line-or.html

sum_digits.py

import timeit
import random

from math import log, ceil


def sum_digits(num):
    sum_dig = 0
    while num > 0:
        last_digit = num % 10 # extract the last digit
        sum_dig += last_digit ** 2 # sum of square of digit
        num /= 10 # strip of last digit
    return sum_dig

def sum_digits2(num):
    return sum(int(digit) ** 2 for digit in str(num))

def sum_digits3(num):
    sum_dig = 0
    while num > 0:
        (num, last) = (num / 10, num % 10)
        sum_dig += last
    return sum_dig

def sum_digits4(num):
    return sum(((num // 10**e) % 10) for e in range(int(ceil(log(num, 10)))))

def test_sum(func):
    func(random.randint(10**10, 10**12))

if __name__ == "__main__":
    reps = 100000
    print(timeit.timeit("test_sum(sum_digits)", setup="from __main__ import test_sum, sum_digits", number=reps))
    print(timeit.timeit("test_sum(sum_digits2)", setup="from __main__ import test_sum, sum_digits2", number=reps))
    print(timeit.timeit("test_sum(sum_digits3)", setup="from __main__ import test_sum, sum_digits3", number=reps))
    print(timeit.timeit("test_sum(sum_digits4)", setup="from __main__ import test_sum, sum_digits4", number=reps))