What dependencies do I need for USB programing in python with pyUSB?

Question

I am trying to get the usb.find command to work properly in a python script I'm writing on Angstrom for the Beagleboard.

Here is my code:

#!/usr/bin/env python

import usb.core 
import usb.util 
import usb.backend.libusb01 as libusb


PYUSB_DEBUG_LEVEL = 'debug'
# find our device
# Bus 002 Device 006: ID 1208:0815
#  idVendor           0x1208
#  idProduct          0x0815
# dev = usb.core.find(idVendor=0xfffe, idProduct=0x0001)
# iManufacturer           1 TOROBOT.com

dev = usb.core.find(idVendor=0x1208, idProduct=0x0815,
backend=libusb.get_backend() )

I don't know what's missing, but here is what I do know. When I don't specify the backend, no backend is found. When I do specify the backend "usb.backend.libusb01" I get the following error:

root@beagleboard:~/servo# ./pyServo.py
Traceback (most recent call last):
  File "./pyServo.py", line 17, in <module>
    dev = usb.core.find(idVendor=0x1208, idProduct=0x0815, backend=libusb.get_backend() )
  File "/usr/lib/python2.6/site-packages/usb/core.py", line 854, in find
    return _interop._next(device_iter(k, v))
  File "/usr/lib/python2.6/site-packages/usb/_interop.py", line 60, in _next
    return next(iter)
  File "/usr/lib/python2.6/site-packages/usb/core.py", line 821, in device_iter
    for dev in backend.enumerate_devices():
  File "/usr/lib/python2.6/site-packages/usb/backend/libusb01.py", line 390, in enumerate_devices
    _check(_lib.usb_find_busses())
  File "/usr/lib/python2.6/ctypes/__init__.py", line 366, in __getattr__
    func = self.__getitem__(name)
  File "/usr/lib/python2.6/ctypes/__init__.py", line 371, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: python: undefined symbol: usb_find_busses

What am I missing so that this will work properly?

Thank you.

Answer 1

Python, pyusb, libusb. I think that's it. Well libc, ld-linux.so too of course, but those are in your system by default.

Do nm -D /path-to/libusb.so and see if usb_find_busses symbol is really there. There's always a chance that your libusb is outdated or somehow specially compiled.

Check if you get any log, for example missing libusb.so should produce something like 'Error loading libusb 0.1 backend'