3桁ごとにコンマを入れる

金額を出すときなんかに3桁ごとにコンマ入れるよね。

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

import sys

def num():
    arg = sys.argv[1]
    leng = len(arg)

    hako = []
    st = ""

    for i in arg:
        hako.append(i)
    lista = hako

    if leng % 3 == 0:
       for i in range(2,leng,3):
           konma = lista[i]+","
           lista[i] = konma
       for i in lista:
           st+=i
    elif leng % 5 == 0:
         for i in range(1,leng,3):
             konma = lista[i]+","
             lista[i] = konma
         for i in lista:
             st+=i
    elif leng % 8 == 0:
         for i in range(1,leng,3):
             konma = lista[i]+","
             lista[i] = konma
         for i in lista:
             st+=i
    else:
         for i in range(0,leng,3):
             konma = lista[i]+","
             lista[i] = konma
         for i in lista:
             st+=i
    print st.rstrip(",")

if __name__ == '__main__':
     num()