题解 | 合法IP

import sys
#十进制转二进制bin(),二进制转十进制int(x,2)
a=input()
if a.count(".")!=3:
    print("NO")
    sys.exit()
else:
    a=a.split(".")
    if a.count("")>0:
        print("NO")
        sys.exit()

    if len(a)!=4:
        print("NO")
        sys.exit()
    else:

        for i in range(len(a)-1):
            if not a[i].isdigit() and len(a[i]) > 1:
                print("NO")
                sys.exit()
            if a[i].startswith('0') and len(a[i]) > 1:
                print("NO")
                sys.exit()
            y=int(a[i])
            if y<0 or y>255:
                print("NO")
                sys.exit()


        y=a[3]   
        if len(y) > 1 and not y[0].isdigit():
            print("NO")
            sys.exit()
        if len(y) > 1 and y[0]=='0':
            print("NO")
            sys.exit()
        if int(y)>=0 and int(y)<=255:
            print('YES')
startswith() 看着题解做的，学到了startswith('0')这个函数