r"""Update an existing descriptor or add a new one.

    dev is the Device object to which the request will be
    sent to.

    The desc parameter is the descriptor to be sent to the device.
    desc_type and desc_index are the descriptor type and index,
    respectively. wIndex index is used for string descriptors
    and represents the Language ID. For other types of descriptors,
    it is zero.

def set_descriptor(dev, desc, desc_type, desc_index, wIndex = None):
    r"""Update an existing descriptor or add a new one.

    dev is the Device object to which the request will be
    sent to.

    The desc parameter is the descriptor to be sent to the device.
    desc_type and desc_index are the descriptor type and index,
    respectively. wIndex index is used for string descriptors
    and represents the Language ID. For other types of descriptors,
    it is zero.
    """
    wValue = desc_index | (desc_type << 8)

    bmRequestType = util.build_request_type(
                        util.CTRL_OUT,
                        util.CTRL_TYPE_STANDARD,
                        util.CTRL_RECIPIENT_DEVICE)

    dev.ctrl_transfer(
        bmRequestType = bmRequestType,
        bRequest = 0x07,
        wValue = wValue,
        wIndex = wIndex,
        data_or_wLength = desc)