I am runing Python 2.7.8 at Win 7 operation system. I am trying to communicate a USB device (Numato 32 channel GPIO device) by PyUSB.
I downloaded walac-pyusb-7071ad3 from URL: http://walac.github.io/pyusb
I stop at receiving "ValueError: No backend available". Could any Python expert tell me where is wrong?
Here is the code:
import sys
import usb
import usb.core
import usb.util
import usb.backend.libusb1
backend = usb.backend.libusb1.get_backend(find_library=lambda C:'\Python27')
numato = usb.core.find(idVendor=00000006,idProduct = 00000000, backend=backend)
Here is Python error message:
Traceback (most recent call last):
File "C:\Python_Yang\PyUSBNumato.py", line 19, in <module>
numato = usb.core.find(idVendor=00000006,idProduct = 00000000, backend=backend)
File "C:\Python_Yang\usb\core.py", line 1199, in find
raise ValueError('No backend available')
ValueError: No backend available
I did: - Download and install libusb-win32-devel-filter-1.2.6.0.exe. It should work.
From:
Pyusb on windows - no backend available
And really works for me.
I had this trouble, and i switched python libusb wrappers and its gone: https://github.com/vpelletier/python-libusb1
I had the same error, but I didn't succeed to use
find_library
(TypeError: get_backend() got an unexpected keyword argument 'find_library'
). I suppose, although you did not say it, thatbackend
is not valid (None
).Do you have the libusb1 implementation in the path
C:\Python27
? I suppose you didn't install it in the Python's folder and if so, there's your answer: PyUSB backend not accessible.Otherwise, without using
find_library
, you must have the libusb1 implementation available in thePATH
environment variable. I did it like this (you can replaceos.getcwd()
with your location):