[pyusb-users] libusb error

[<sr...@li...>]

Dear Sirs,
I have tried to use pyusb module and I have used a script in order to test it, but the script terminates with an error:
2017-01-26 07:46:41,662 ERROR:usb.libloader:'Libusb 1' could not be found2017-01-26 07:46:41,685 ERROR:usb.backend.libusb1:Error loading libusb 1.0 backend2017-01-26 07:46:41,795 ERROR:usb.libloader:'OpenUSB library' could not be found2017-01-26 07:46:41,804 ERROR:usb.backend.openusb:Error loading OpenUSB backend2017-01-26 07:46:42,098 ERROR:usb.libloader:'Libusb 0' could not be found2017-01-26 07:46:42,108 ERROR:usb.backend.libusb0:Error loading libusb 0.1 backendTraceback (most recent call last):  File "./usbtest.py", line 13, in <module>    dev = usb.core.find(find_all=True)  File "/root/Buildroot/output/target/usr/lib/python3.4/site-packages/usb/core.py", line 1263, in findusb.core.NoBackendError: No backend available

libusb is already installed on the system, but it seems that it is not seen by the module.
How can I fix this problem?
Thanking you in advance,
Simone Rossi