def connack_string(connack_code):
    """Return the string associated with a CONNACK result."""
    if connack_code == 0:
        return 'Connection Accepted.'
    elif connack_code == 1:
        return 'Connection Refused: unacceptable protocol version.'
    elif connack_code == 2:
        return 'Connection Refused: identifier rejected.'
    elif connack_code == 3:
        return 'Connection Refused: broker unavailable.'
    elif connack_code == 4:
        return 'Connection Refused: bad user name or password.'
    elif connack_code == 5:
        return 'Connection Refused: not authorised.'
    else:
        return 'Connection Refused: unknown reason.'
