formatter.py

# -*- coding: utf-8 -*-


def formatter(n):
    n = list(str(n))[::-1]
    n = ','.join([
        ''.join(n[index:index+3])
        for index in range(0, len(n), 3)
    ])[::-1]
    print n

formatter(1234567890)
formatter(123456789)
formatter(12345678)
formatter(1234567)
formatter(123456)
formatter(12345)
formatter(1234)
formatter(123)
formatter(12)
formatter(1)
formatter(35235235)
formatter(100)
formatter(999999999)