I need help to call a function(Struct C) that detects the devices, so I'm calling the function this way:

from ctypes import *
fp = CDLL('./libfprint.so.0')
fp.fp_discover_devs.argtypes = None
fp.fp_discover_devs.restype = c_char_p
ret = fp.fp_discover_devs()
print ret # is "0" 

That is not detected any device, because the return is "0".

See the documentation of the function:

I'm using Ubuntu and I downloaded the "fprint_demo" and works perfectly. Did you install any package missing?

Thanks.