OSError with wxPython

If I try to find the USB devices in a wxPython window, I get the following error:

Exception ignored in: <bound method _AutoFinalizedObjectBase.__del__ of <usb.backend.libusb1._Device object at 0x04307210>>
Traceback (most recent call last):
  File "C:\Users\guest\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\_objfinalizer.py", line 84, in __del__
    self.finalize()
  File "C:\Users\guest\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\_objfinalizer.py", line 144, in finalize
    self._finalizer()
  File "C:\Users\guest\AppData\Local\Programs\Python\Python36-32\lib\weakref.py", line 548, in __call__
    return info.func(*info.args, **(info.kwargs or {}))
  File "C:\Users\guest\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\_objfinalizer.py", line 104, in _do_finalize_object_ref
    obj._do_finalize_object()
  File "C:\Users\guest\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\_objfinalizer.py", line 71, in _do_finalize_object
    self._finalize_object()
  File "C:\Users\guest\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\backend\libusb1.py", line 604, in _finalize_object
    _lib.libusb_unref_device(self.devid)
OSError: exception: access violation writing 0x00000014
^C

Here is some simple code that can create the error.

import wx
import usb

class MyForm(wx.Frame):
	def __init__(self):
		wx.Frame.__init__(self, None, wx.ID_ANY, "Example")
		panel = wx.Panel(self, wx.ID_ANY)
		sizer = wx.BoxSizer(wx.VERTICAL)

		button = wx.Button(panel, label="Run test()")
		button.Bind(wx.EVT_BUTTON, self.test)
		
		sizer.Add(button, 0, wx.ALL|wx.CENTER, 5)
		panel.SetSizer(sizer)

	def test(self, event):
		valueList = []
		devices = usb.core.find(find_all=True)
		for config in devices:
			valueList.append((config.idVendor, config.idProduct))
		print(valueList)

		event.Skip()

if __name__ == "__main__":
	app = wx.App(False)
	frame = MyForm()
	frame.Show()
	app.MainLoop()

To produce the error, press the button “Run test()” in the frame that appears after running the code.

[jonasmalacofilho]

@JoshMayberry

This fix is not, however, in the latest version on pypi.org.

I understand (including from my own experience) that this is an annoying issue for downstream projects. I’ll try to get a release ready soon, even if some other issues end up missing the cut.

[mcuee]

Maybe the following can help.

Ref: https://github.com/eblot/pyftdi/issues/121 eblot commented:

I found a weird behaviour in pyusb: when the port is indirectly closed right after the port is open, some kind of race condition in pyusb/libusb lets it to re-open the closed device to perform the cleanup action, which triggers a native exception in libusb. This has been worked around in the latest PyFtdi patch version (v0.30.1), so that no cleanup action is performed when the existing pyusb handle is not longer existing. This prevents the pyusb resource manager to re-open the device in such event.