hid.find_all_hid_devices() in asyncio coroutine

Question

In order to access a a USB HID device connected on my computer I use the function find_all_hid_devices()from the pywinusb package.

Now I would like to access this HID device from an asyncio coroutine. With the following code

@asyncio.coroutine
def main():
    from pywinusb import hid
    a = hid.find_all_hid_devices()

The following error is returned:

Traceback (most recent call last):
  File "C:\Python34\lib\site-packages\pywinusb\hid\core.py", line 122, in find_all_hid_devices
    for interface_data in winapi.enum_device_interfaces(h_info, guid):
  File "C:\Python34\lib\site-packages\pywinusb\hid\winapi.py", line 466, in enum_device_interfaces
    byref(dev_interface_data) ):
ctypes.ArgumentError: argument 1: <class 'OverflowError'>: int too long to convert

The same call to hid.find_all_hid_devices() however works on its own, in a plain main without asyncio.

Is this due to the fact that I'm trying to access within a coroutine? What is the proper way to achieve this?

Answer 1

pywinusb library is synchronous by design, thus you should call it in thread pool.

@asyncio.coroutine
def f():
    loop = asyncio.get_event_loop()
    a = yield from loop.run_in_executor(None, hid.find_all_hid_devices)

Synchronous call from coroutine is allowed technically but discouraged because it pauses event loop for long time period.