Python PyUSB没有后端可用，即使路径中有dll，也显式加载

尽管我在路径中安装了libusb1，并在代码的前面很好地加载了libusb1，但我在pyusb中收到了一个no-backend错误。我的代码是

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')

运行此代码将返回

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

不会返回错误。更奇怪的是，背景

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

并在调试器中执行，返回值为None的backend。有没有好办法解决这个问题？如果有帮助的话，我正在使用Windows7

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