Docs for IS_IPV4

    Checks if field's value is an IP version 4 address in decimal form. Can
    be set to force addresses from certain range.

    IPv4 regex taken from: http://regexlib.com/REDetails.aspx?regexp_id=1411

    Args:

        minip: lowest allowed address; accepts:

            - str, eg. 192.168.0.1
            - list or tuple of octets, eg. [192, 168, 0, 1]
        maxip: highest allowed address; same as above
        invert: True to allow addresses only from outside of given range; note
            that range boundaries are not matched this way
        is_localhost: localhost address treatment:

            - None (default): indifferent
            - True (enforce): query address must match localhost address (127.0.0.1)
            - False (forbid): query address must not match localhost address
        is_private: same as above, except that query address is checked against
            two address ranges: 172.16.0.0 - 172.31.255.255 and
            192.168.0.0 - 192.168.255.255
        is_automatic: same as above, except that query address is checked against
            one address range: 169.254.0.0 - 169.254.255.255

    Minip and maxip may also be lists or tuples of addresses in all above
    forms (str, int, list / tuple), allowing setup of multiple address ranges::

        minip = (minip1, minip2, ... minipN)
                   |       |           |
                   |       |           |
        maxip = (maxip1, maxip2, ... maxipN)

    Longer iterable will be truncated to match length of shorter one.

    Examples:
        Check for valid IPv4 address:

            INPUT(_type='text', _name='name', requires=IS_IPV4())

        Check for valid IPv4 address belonging to specific range:

            INPUT(_type='text', _name='name',
                requires=IS_IPV4(minip='100.200.0.0', maxip='100.200.255.255'))

        Check for valid IPv4 address belonging to either 100.110.0.0 -
        100.110.255.255 or 200.50.0.0 - 200.50.0.255 address range:

            INPUT(_type='text', _name='name',
                requires=IS_IPV4(minip=('100.110.0.0', '200.50.0.0'),
                             maxip=('100.110.255.255', '200.50.0.255')))

        Check for valid IPv4 address belonging to private address space:

            INPUT(_type='text', _name='name', requires=IS_IPV4(is_private=True))

        Check for valid IPv4 address that is not a localhost address:

            INPUT(_type='text', _name='name', requires=IS_IPV4(is_localhost=False))

            >>> IS_IPV4()('1.2.3.4')
            ('1.2.3.4', None)
            >>> IS_IPV4()('255.255.255.255')
            ('255.255.255.255', None)
            >>> IS_IPV4()('1.2.3.4 ')
            ('1.2.3.4 ', 'enter valid IPv4 address')
            >>> IS_IPV4()('1.2.3.4.5')
            ('1.2.3.4.5', 'enter valid IPv4 address')
            >>> IS_IPV4()('123.123')
            ('123.123', 'enter valid IPv4 address')
            >>> IS_IPV4()('1111.2.3.4')
            ('1111.2.3.4', 'enter valid IPv4 address')
            >>> IS_IPV4()('0111.2.3.4')
            ('0111.2.3.4', 'enter valid IPv4 address')
            >>> IS_IPV4()('256.2.3.4')
            ('256.2.3.4', 'enter valid IPv4 address')
            >>> IS_IPV4()('300.2.3.4')
            ('300.2.3.4', 'enter valid IPv4 address')
            >>> IS_IPV4(minip='1.2.3.4', maxip='1.2.3.4')('1.2.3.4')
            ('1.2.3.4', None)
            >>> IS_IPV4(minip='1.2.3.5', maxip='1.2.3.9', error_message='Bad ip')('1.2.3.4')
            ('1.2.3.4', 'bad ip')
            >>> IS_IPV4(maxip='1.2.3.4', invert=True)('127.0.0.1')
            ('127.0.0.1', None)
            >>> IS_IPV4(maxip='1.2.3.4', invert=True)('1.2.3.4')
            ('1.2.3.4', 'enter valid IPv4 address')
            >>> IS_IPV4(is_localhost=True)('127.0.0.1')
            ('127.0.0.1', None)
            >>> IS_IPV4(is_localhost=True)('1.2.3.4')
            ('1.2.3.4', 'enter valid IPv4 address')
            >>> IS_IPV4(is_localhost=False)('127.0.0.1')
            ('127.0.0.1', 'enter valid IPv4 address')
            >>> IS_IPV4(maxip='100.0.0.0', is_localhost=True)('127.0.0.1')
            ('127.0.0.1', 'enter valid IPv4 address')