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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_valid_ipv4 (ip):
 """ Return True if given ip is a valid IPv4 address. """

    if not _ipv4_re.match(ip):
        return False
    a, b, c, d = [int(i) for i in ip.split(".")]
    return a <= 255 and b <= 255 and c <= 255 and d <= 255