一個剛結束的筆試題目，簡單貼一下吧，下面是具體實現：

#!usr/bin/env python
#encoding:utf-8

'''
__Author__:沂水寒城
功能：判斷一個字串是否是合法IP地址
'''


import re


def judge_legal_ip(one_str):
    '''
    正則匹配方法
    判斷一個字串是否是合法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):
    '''
    簡單的字串判斷
    '''
    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):  #正則方法
        #if judge_legal_ip2(one_str):  #字串方法
            print '{0} is a legal ip address!'.format(one_str)
        else:
            print '{0} is not a legal ip address!'.format(one_str)
 

結果如下：

 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!