CODEWITHSUNDEEP
pythonpathusbpyusblibusb-1.0
bever
bever

Reputation: 33

PyUSB no backend available even with dll in path, explicitly loaded

I'm receiving a no backend error in pyusb despite the fact that I have LibUSB 1 installed, in the path, and loaded fine earlier in the code. My code is

import usb.core
import usb.util
import usb.backend.libusb1
import sys

class USBConnection:
def __init__(self, vendor_id, product_id):
    usb.backend.libusb1.get_backend(find_library=lambda x: 'C:\Windows\System32\libusb-1.0.dll')
    self.device = usb.core.find(idVendor=vendor_id, idProduct=product_id)
    if self.device is None:
        sys.exit('Could not find device')
    else:
        print 'Device detected'
    self.device.set_configuration()
    self.configuration = self.device.get_active_configuration()
    self.description = self.configuration[(0, 0)]
    self.end_point = usb.util.find_descriptor(self.description, custome_match=lambda e: usb.util.endpoint_direction
                                              (e.bEndpointAddress) == usb.util.ENDPOINT_OUT)
    assert self.end_point is not None

def write(self, data):
    self.end_point.write(data)

if __name__ == '__main__':
    channel = USBConnection(vendor_id='2A19', product_id='1002')

Running this code returns

Traceback (most recent call last):
  File "C:/Users/me/PycharmProjects/usbfreqsweep/usbsweep.py", line 126, in <module>
channel = USBConnection(vendor_id='2A19', product_id='1002')
  File "C:/Users/me/PycharmProjects/usbfreqsweep/usbsweep.py", line 110, in __init__
self.device = usb.core.find(idVendor=vendor_id, idProduct=product_id)
  File "C:\Python27\lib\site-packages\usb\core.py", line 1263, in find
raise NoBackendError('No backend available')
usb.core.NoBackendError: No backend available

I do in fact have the C:\windows\system32 in my path with llibusb-1.0.dll contained and the most recent version of libusb1 installed, but I still get this error. This is in spite of the fact that 

    usb.backend.libusb1.get_backend(find_library=lambda x: 'C:\Windows\System32\libusb-1.0.dll')

does not return an error. Even weirder, setting 

backend = usb.backend.libusb1.get_backend(find_library=lambda x: 'C:\Windows\System32\libusb-1.0.dll')

and going through in the debugger returns backend with a value of None. Is there a good way to fix this? I'm using Windows 7, if that helps.

Upvotes: 3

Views: 1163

Answers (1)

金京光
金京光

Reputation: 1

  1. bk = usb.backend.libusb1.get_backend(find_library=lambda x: 'C:\Windows\System32\libusb-1.0.dll')
  2. self.device = usb.core.find(idVendor=vendor_id, idProduct=product_id) to self.device = usb.core.find(backend=bk,idVendor=vendor_id, idProduct=product_id)

Upvotes: 0

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