python如何判断IP地址合法性

import os,sys
a=input()
def check_ip(ip): 
  import sys 
  sc=ip.strip().split('.') 
  if len(sc)!= 4: 
    print( "check ip address failed!")
    sys.exit()
  for i in range(4):
   b=len(sc[i])
   c=sc[i]
   for j in range(b):
    if c[j]==" ":
     print ("check ip address failed!")
     sys.exit()
   j+=1  
   try:
    sc[i]=int(sc[i]) 
   except: 
    print ("check ip address failed!")
    sys.exit()
   if sc[i]<=255 & sc[i]>=0:  
    pass
   else:
    print ("check ip address failed!")
    sys.exit() 
   i+=1
  else: 
    print ("check ip address success!")
  if len(sys.argv)!=2: 
   print ("Example: %s 10.0.0.1 "%sys.argv[0] )
   sys.exit() 
  else: 
   check_ip(sys.argv[1]) 
print(check_ip(a))