Pyusb on windows - no backend available

Question

I\'m trying to have my python application interface with an NFC device via USB. The best option seems to be pyusb, but I can\'t get it to connect to the libusb backend. I ke

Answer 1

I am using Python 2.6.5, libusb-win32-device.bin-0.1.12.1 and pyusb-1.0.0-a0 on a windows XP system and kept receiving ValueError: No backend available.

Since there wasn't any real help on the web for this problem I spent a lot of time finding that ctypes util.py uses the Path variable to find the library file. My path did not include windows\system32 and PYUSB didn't find the library. I updated the path variable and now the USB is working.

Answer 2

1. download the latest libusb Download libusb

Copy MS32\dll\libusb-1.0.dll to C:\Windows\SysWOW64

Copy MS64\dll\libusb-1.0.dll to C:\Windows\System32

3.

pip install libusb

Copy MS32\dll\libusb-1.0.dll to C:\Python\Python37-32\Lib\site-packages\libusb_platform_windows\x86

Copy MS64\dll\libusb-1.0.dll to C:\Python\Python37-32\Lib\site-packages\libusb_platform_windows\x64

This method works for me.

Answer 3

To connect to your NFC device via USB using PYUSB, you will need to install the backend for that device. I do not think there is any backend for any device other than a libusb device.

To build a backend. You will need to know the driver (.sys file) for your device, so you could write a wrapper DLL to expose functionalities in the device. Your DLL would have to have a method to find device based on PID & VID, another method to open device and another method to send data and so on...

Answer 4

Download and install libusb-win32-devel-filter-1.2.6.0.exe. It should work.

Answer 5

There's a simpler solution.

Download and unpack to C:\PATH the libusb-1.0.20 from download link

Then try this line:

backend = usb.backend.libusb1.get_backend(find_library=lambda x: "C:\PATH\libusb-1.0.20\MS32\dll\libusb-1.0.dll")

dev = usb.core.find(backend=backend, find_all=True)

Depending on your system, try either MS64 or MS32 version of the .dll

Update of 17/01/2020, after a request to share more code:

import usb.core
import usb.util

from infi.devicemanager import DeviceManager
dm = DeviceManager()
devices = dm.all_devices
for i in devices:
    try:
        print ('{} : address: {}, bus: {}, location: {}'.format(i.friendly_name, i.address, i.bus_number, i.location))
    except Exception:
        pass


import usb.backend.libusb1

backend = usb.backend.libusb1.get_backend(find_library=lambda x: "C:\\libusb-1.0.20\\MS32\\dll\\libusb-1.0.dll")
dev = usb.core.find(backend=backend, find_all=True)

def EnumerateUSB():    #I use a simple function that scans all known USB connections and saves their info in the file
    with open("EnumerateUSBLog.txt", "w") as wf:
        counter = 0
        for d in dev:
            try:
                wf.write("USB Device number " + str(counter) + ":" + "\n")
                wf.write(d._get_full_descriptor_str() + "\n")
                wf.write(d.get_active_configuration() + "\n")
                wf.write("\n")
                counter += 1
            except NotImplementedError:
                wf.write("Device number " + str(counter) + "is busy." + "\n")
                wf.write("\n")
                counter += 1
            except usb.core.USBError:
                wf.write("Device number " + str(counter) + " is either disconnected or not found." + "\n")
                wf.write("\n")
                counter += 1
        wf.close()

Answer 6

I had the same problem with Windows 10, both Python 2.7.16 and Python 3.7.2. I installed libusb (through python -m pip install libusb ) but the error message remained. Also, the advice above about installing libusb-win32 did not work for me; neither of the 2 links (original post and @beebek's answer) existed.

What did work, however, is the comment by @user1495323 : I copied libusb-1.0.dll from C:\Users\username\AppData\Roaming\Python\Python27\site-packages\libusb\_platform\_windows\x64\ to C:\Windows\System32\