def host_type(host):
    """
    Correctly classify correct RFC 3986 compliant hostnames, but do not try
    hard to validate compliance anyway...
    NOTE: indeed we allow a small deviation from the RFC 3986: IPv4
    addresses are allowed to contain bytes represented in hexadecimal or
    octal notation when begining respectively with '0x'/'0X' and '0'
    numbers prepended with one or more zero won't be rejected.  Anyway
    representation of multiple bytes by a single decimal/octal/hexadecimal
    integer is not allowed.

    Return 1 (HOST_IP_LITERAL), 2 (HOST_IPV4_ADDRESS) or 3 (HOST_REG_NAME)

    >>> host_type('[blablabla]')
    1
    >>> host_type('')
    3
    >>> host_type('127.0.0.1')
    2
    >>> host_type('0x7F.0.0.00000000000001')
    2
    >>> host_type('666.42.131.2')
    3
    >>> host_type('foobar.42')
    3
    """
    if not host:
        return HOST_REG_NAME
    elif host[0] == '[':
        return HOST_IP_LITERAL
    elif __valid_IPv4address(host):
        return HOST_IPV4_ADDRESS
    else:
        return HOST_REG_NAME