不允许进行python操作（graphtecprint）

Question

I'm running a python program. When it get's to these lines:
f = open("/dev/bus/usb/007/005", "r")
x = fcntl.ioctl(f.fileno(), 0x84005001, '\\x00' * 256)
It fails saying:
IOError: [Errno 1] Operation not permitted
What could be causing this problem?

Answer 1

file system permissions?

what does ls -l /dev/bus/usb/007/005 say?

does cat /dev/bus/usb/007/005 work or does it report the same error?

Answer 2

The third argument to fcntl.ioctl , as documented here , should be either a 1024-byte string (not just 256), or, better, a possibly even-larger writeable buffer -- the underlying object could be an array.array of bytes. Unfortunately you need to know in advance how much space the result will need, but you can play it safe with a few KB (that ioctl seems to be the "get device id" code, but I'm not sure what the max result length could be).