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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 AAAA(host, nameserver=None):
    '''
    Return the AAAA record for ``host``.

    Always returns a list.

    CLI Example:

    .. code-block:: bash

        salt ns1 dig.AAAA www.google.com
    '''
    dig = ['dig', '+short', six.text_type(host), 'AAAA']

    if nameserver is not None:
        dig.append('@{0}'.format(nameserver))

    cmd = __salt__['cmd.run_all'](dig, python_shell=False)
    # In this case, 0 is not the same as False
    if cmd['retcode'] != 0:
        log.warning(
            'dig returned exit code \'%s\'. Returning empty list as fallback.',
            cmd['retcode']
        )
        return []

    # make sure all entries are IPs
    return [x for x in cmd['stdout'].split('\n') if check_ip(x)]