def valid_port(port):
    """
    Returns True if `port` is a valid port.

    **Example usage**

    >>> assert(not valid_port(-1))
    >>> assert(not valid_port('something not a port'))
    >>> assert(valid_port('80'))
    >>> valid_port(65535)
    True
    """
    try:
        return 0 <= int(port) < 2 ** 16
    except:
        return False
