returns valid COM Port.

def check_serial_port(name):
    """returns valid COM Port."""
    try:
        cdc = next(serial.tools.list_ports.grep(name))
        return cdc[0]
    except StopIteration:
        msg = "device {} not found. ".format(name)
        msg += "available devices are: "
        ports = list(serial.tools.list_ports.comports())
        for p in ports:
            msg += "{},".format(text_type(p))
        raise ValueError(msg)