title: PyUSB dev.set_configuration()
body: <p>I am trying to send data to a usb stick using the python library PyUSB. The code I am using is the following:</p>
  
  <pre><code>import usb.core
  import usb.util
  
  # find our devices
  #dev = usb.core.find(idVendor=0xfffe, idProduct=0x0001)
  dev = usb.core.find(idVendor=0x090c, idProduct=0x1000)
  
  # was it found?
  if dev is None:
      raise ValueError('Device not found')
  
  # set the active configuration. With no arguments, the first
  # configuration will be the active one
  dev.set_configuration()
  
  # get an endpoint instance
  cfg = dev.get_active_configuration()
  interface_number = cfg[(0,0)].bInterface_number
  alternate_setting = usb.control.get_interface(interface_number)
  intf = usb.util.find_descriptor(
      cfg, bTnerfaceNumber = interface_number,
      bAlternateSettings = alternate_setting
  )
  
  ep = usb.util.find_descriptor(
      intf,
      # match the first OUT endpoint
      custom_match = \
      lambda e:
          usb.util.endpoint_direction(e.bEndpointAddress) == \
          usb.util.ENDPOINT_OUT
  )
  
  assert ep is not None
  
  # write the data
  ep.write('test')
  </code></pre>
  
  <p>however I seem to be getting the following error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/home/usman/Desktop/c_code/libusb_test_data/pyusb_code/send_data_rev_one.py", line 14, in &lt;module&gt;
      dev.set_configuration()
    File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 554, in set_configuration
      self._ctx.managed_set_configuration(self, configuration)
    File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 91, in managed_set_configuration
      self.managed_open()
    File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 70, in managed_open
      self.handle = self.backend.open_device(self.dev)
    File "/usr/local/lib/python2.7/dist-packages/usb/backend/libusb1.py", line 494, in open_device
      _check(_lib.libusb_open(dev.devid, byref(handle)))
    File "/usr/local/lib/python2.7/dist-packages/usb/backend/libusb1.py", line 403, in _check
      raise USBError(_str_error[ret], ret, _libusb_errno[ret])
  USBError: [Errno 13] Access denied (insufficient permissions)
  </code></pre>
  
  <p>can somebody walk me through this error and tell me how to fix it</p>
  
  <p>thanks</p>