python实现判断一个字符串是否是合法IP地址

#!usr/bin/env python
#encoding:utf-8
'''
__Author__:沂水寒城
功能：判断一个字符串是否是合法IP地址
'''
import re
def judge_legal_ip(one_str):
  '''
  正则匹配方法
  判断一个字符串是否是合法IP地址
  '''
  compile_ip=re.compile('^((25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(25[0-5]|2[0-4]\d|[01]?\d\d?)$') 
  if compile_ip.match(one_str): 
    return True 
  else: 
    return False 
def judge_legal_ip2(one_str):
  '''
  简单的字符串判断
  '''
  if '.' not in one_str:
    return False
  elif one_str.count('.')!=3:
    return False
  else:
    flag=True
    one_list=one_str.split('.')
    for one in one_list:
      try:
        one_num=int(one)
        if one_num>=0 and one_num<=255:
          pass
        else:
          flag=False
      except:
        flag=False
    return flag
          
if __name__=='__main__':
  ip_list=['','172.31.137.251','100.10.0.1000','1.1.1.1','12.23.13','aa.12.1.2','12345678','289043jdhjkbh']
  for one_str in ip_list:
    if judge_legal_ip(one_str): #正则方法
    #if judge_legal_ip2(one_str): #字符串方法
      print '{0} is a legal ip address!'.format(one_str)
    else:
      print '{0} is not a legal ip address!'.format(one_str)

is not a legal ip address! 
172.31.137.251 is a legal ip address! 
100.10.0.1000 is not a legal ip address! 
1.1.1.1 is a legal ip address! 
12.23.13 is not a legal ip address! 
aa.12.1.2 is not a legal ip address! 
12345678 is not a legal ip address! 
289043jdhjkbh is not a legal ip address!