import re

octet = r'(?:[0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])'
rx = re.compile(r"\A{0}(?:\.{0}){{3}}\Z".format(octet))

def ipv4_address(ip):
        return bool(rx.match(ip))

strs = ["127.0.0.1\n","127.0.0.2"]
for s in strs:
    print("'{}' => {}".format(s, ipv4_address(s)))