Sending USB commands with Python

[MRAB]

On 30/08/2012 00:45, Adam W. wrote:
> On Wednesday, August 29, 2012 6:56:16 PM UTC-4, Dennis Lee Bieber wrote:
>>
>> 	BUT you do give a possible clue. Is the OP using a 3.x Python where
>>
>> strings are Unicode -- in which case the above may need to be explicitly
>>
>> declared as a "byte string" rather than text (unicode) string.
>>
>
> Huzzah!  I am indeed using 3.x, and slapping on an .encode('utf-8') made my printer try to spit paper at me! Progress.
>
> Also, astute observation about the endpoint needing to be an input, with the following modification I get:
>
>>>> ep.write('\x1BA'.encode('utf-8'))
> 2
>>>> ep = usb.util.find_descriptor(
>      intf,
>      custom_match = \
>      lambda e: \
>          usb.util.endpoint_direction(e.bEndpointAddress) == \
>          usb.util.ENDPOINT_IN
> )
>>>> ep.read(1)
> array('B', [163])
>>>>
>
> Anyone want to venture a guess on how I should interpret that?  It seems the [163] is the byte data the manual is talking about, but why is there a 'B' there?  If I put paper in it and try again I get: array('B', [3])
>
> Thanks for all your help guys, just about ready to stared coding the fun part!
>
The result is an array of bytes ('B'). I think the value means:

0b10100011
          ^Ready
         ^Top of form
     ^No paper
   ^Printer error

The error is that it's out of paper.