title: PyUSB ValueError: No backend available
body: <p>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. </p>
  
  <p>I downloaded walac-pyusb-7071ad3 from URL: <a href="http://walac.github.io/pyusb" rel="nofollow">http://walac.github.io/pyusb</a>   </p>
  
  <p>I stop at receiving "ValueError: No backend available". Could any Python expert tell me where is wrong?</p>
  
  <p>Here is the code:</p>
  
  <pre><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)
  </code></pre>
  
  <p>Here is Python error message:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Python_Yang\PyUSBNumato.py", line 19, in &lt;module&gt;
      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
  </code></pre>