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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Sending USB commands with Python
Date: Wed, 29 Aug 2012 22:07:36 -0400
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On Wed, 29 Aug 2012 16:45:10 -0700 (PDT), "Adam W."
<AWasilenko@gmail.com> declaimed the following in
gmane.comp.python.general:

> 
> 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

	I'm a tad curious if using the notation

		b'\x1bA'

without the .encode() would work.

	My concern is that you may encounter some "string" of data for
printing which the .encode() ends up /changing/ (don't UTF-8 strings use
a high-bit to signal a multi-byte encoding of what had been a single
character?). A pure byte string shouldn't have that problem.

> >>> ep = usb.util.find_descriptor(
>     intf,
>     custom_match = \
>     lambda e: \
>         usb.util.endpoint_direction(e.bEndpointAddress) == \
>         usb.util.ENDPOINT_IN
> )

	Seems tedious to keep swapping -- does USB support bidirectional
connections?

> >>> 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])

	Per documentation (section 8.6 in Python 2.7.2 library) of "array"
module:

'b' signed char int 1 
'B' unsigned char int 1 


>>> import array
>>> array.array("B", "\x1bB")
array('B', [27, 66])
>>> 
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
        wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/