usb-Zugriff uner python geht ncht wie erwartet

Beim Zugriff auf das (angeschlossene) usb-device erhalte ich folgende 
Fehlermeldung:
----------------------------------------
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File 
"/usr/lib/python2.7/dist-packages/spyderlib/widgets/externalshell/sitecu 
stomize.py",  line 540, in runfile
    execfile(filename, namespace)
  File "/home/rfr/workspace/python/testUSBaccess.py", line 9, in 
<module>
    raise ValueError('Device not found')
ValueError: Device not found
>>> runfile('/home/rfr/workspace/python/testUSBaccess.py', 
wdir=r'/home/rfr/workspace/python')
DEVICE ID 173a:2198 on Bus 002 Address 011 =================
 bLength                :   0x12 (18 bytes)
 bDescriptorType        :    0x1 Device
 bcdUSB                 :  0x200 USB 2.0
 bDeviceClass           :    0x0 Specified at interface
 bDeviceSubClass        :    0x0
 bDeviceProtocol        :    0x0
 bMaxPacketSize0        :   0x20 (32 bytes)
 idVendor               : 0x173a
 idProduct              : 0x2198
 bcdDevice              :  0x100 Device 1.0
 iManufacturer          :    0x1 Error Accessing String
 iProduct               :    0x2 Error Accessing String
 iSerialNumber          :    0x3 Error Accessing String
 bNumConfigurations     :    0x1
  CONFIGURATION 1: 102 mA ==================================
   bLength              :    0x9 (9 bytes)
   bDescriptorType      :    0x2 Configuration
   wTotalLength         :   0x20 (32 bytes)
   bNumInterfaces       :    0x1
   bConfigurationValue  :    0x1
   iConfiguration       :    0x0
   bmAttributes         :   0x80 Bus Powered
   bMaxPower            :   0x33 (102 mA)
    INTERFACE 0: Mass Storage ==============================
     bLength            :    0x9 (9 bytes)
     bDescriptorType    :    0x4 Interface
     bInterfaceNumber   :    0x0
     bAlternateSetting  :    0x0
     bNumEndpoints      :    0x2
     bInterfaceClass    :    0x8 Mass Storage
     bInterfaceSubClass :    0x6
     bInterfaceProtocol :   0x50
     iInterface         :    0x0
      ENDPOINT 0x81: Bulk IN ===============================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :   0x81 IN
       bmAttributes     :    0x2 Bulk
       wMaxPacketSize   :   0x40 (64 bytes)
       bInterval        :    0x0
      ENDPOINT 0x2: Bulk OUT ===============================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :    0x2 OUT
       bmAttributes     :    0x2 Bulk
       wMaxPacketSize   :   0x40 (64 bytes)
       bInterval        :    0x0
EINS
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File 
"/usr/lib/python2.7/dist-packages/spyderlib/widgets/externalshell/sitecu 
stomize.py",  line 540, in runfile
    execfile(filename, namespace)
  File "/home/rfr/workspace/python/testUSBaccess.py", line 13, in 
<module>
    dev.set_configuration()
  File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 799, 
in set_configuration
    self._ctx.managed_set_configuration(self, configuration)
  File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 127, 
in managed_set_configuration
    self.managed_open()
  File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 105, 
in managed_open
    self.handle = self.backend.open_device(self.dev)
  File "/usr/local/lib/python2.7/dist-packages/usb/backend/libusb1.py", 
line 722, in open_device
    return _DeviceHandle(dev)
  File "/usr/local/lib/python2.7/dist-packages/usb/backend/libusb1.py", 
line 600, in _init_
    _check(_lib.libusb_open(self.devid, byref(self.handle)))
  File "/usr/local/lib/python2.7/dist-packages/usb/backend/libusb1.py", 
line 552, in _check
    raise USBError(_strerror(ret), ret, _libusb_errno[ret])
usb.core.USBError: [Errno 13] Access denied (insufficient permissions)
>>>
-----------------------------------
den folgende Source produziert:
_--------------------------
import usb.core
import usb.util

# find our device
dev = usb.core.find(idVendor=0x173a, idProduct=0x2198)
print dev
# was it found?
if dev is None:
    raise ValueError('Device not found')
print 'EINS'
# 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()
intf = cfg[(0,0)]

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')
------------------------------------
Dazu folgende Fragen:

wie kann ich das Programm so schreiben, dass verschiedene IdVendors und 
IdProduct numbers erkannt werden können?

Was genau sagt mir die Fehlermeldung?

Grüsse

Robert