判断IP是否合法

import sys,os

def ipcheck(ipstr):
    tag=True
    bb=ipstr.split(\'.\',4)
    if len(ipstr.split(\'.\',4))!=4:
        tag=False
        print("不是合法的IP地址")
    else:
        for i in range(len(bb)):
            if bb[i].isdigit() != 0 and 0 <= int(bb[i]) <= 255:
                if len(bb[i])>1 and bb[i][0]!=0:
                    tag=False
                    print("不是合法的IP地址")
                else:
                    tag=True
            else:
                tag = False
                print("不是合法的IP地址2")
                sys.exit()
    return tag
ipcheck("01.0.1.0")