Python数字加千分符

1、最简单的内置format函数：

>>> format(1234567890,',')
'1,234,567,890'

2、正则表达式：

import re
def formatNum(num):
    num=str(num)
    pattern=r'(\d+)(\d{3})((,\d{3})*)'
    while True:
        num,count=re.subn(pattern,r'\1,\2\3',num)
        if count==0:
            break
    return num
if __name__=='__main__':
    print formatNum(1234455)

3、最笨的倒置后遍历过三位加逗号：

def formatNum(num):
    num=str(num)
    result=''
    count=0
    for i in num[::-1]:
        count+=1
        result+=i
        if count%3==0:
            result+=','  
    return result[::-1].strip(',')
if __name__=='__main__':
    print formatNum(123445)