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From: johnty on 2 Jun 2010 02:43
i'm reading bytes from a serial port, and storing it into an array.

each byte represents a signed 8-bit int.

currently, the code i'm looking at converts them to an unsigned int by
doing ord(array[i]). however, what i'd like is to get the _signed_
integer value. whats the easiest way to do this?

thanks in advance.

johnty
From: Stefan Behnel on 2 Jun 2010 03:01
johnty, 02.06.2010 08:43:
> i'm reading bytes from a serial port, and storing it into an array.
>
> each byte represents a signed 8-bit int.
>
> currently, the code i'm looking at converts them to an unsigned int by
> doing ord(array[i]). however, what i'd like is to get the _signed_
> integer value. whats the easiest way to do this?

See the struct module, it supports various different C types.

Stefan

From: Steven D'Aprano on 2 Jun 2010 03:03
On Tue, 01 Jun 2010 23:43:33 -0700, johnty wrote:

> i'm reading bytes from a serial port, and storing it into an array.

An array or a list?


> each byte represents a signed 8-bit int.
>
> currently, the code i'm looking at converts them to an unsigned int by
> doing ord(array[i]). however, what i'd like is to get the _signed_
> integer value. whats the easiest way to do this?

>>> import array
>>> s = 'Some unsigned bytes \xc3\x80\xc3\xa0\xc3\xa6\xc3\x9f\xc2\xb5'
>>> array.array('b', s)
array('b', [83, 111, 109, 101, 32, 117, 110, 115, 105, 103, 110, 101,
100, 32, 98, 121, 116, 101, 115, 32, -61, -128, -61, -96, -61, -90, -61,
-97, -62, -75])


See also the fromstring method of array objects.


--
Steven
From: Christian Heimes on 2 Jun 2010 03:04
> i'm reading bytes from a serial port, and storing it into an array.
>
> each byte represents a signed 8-bit int.
>
> currently, the code i'm looking at converts them to an unsigned int by
> doing ord(array[i]). however, what i'd like is to get the _signed_
> integer value. whats the easiest way to do this?

http://docs.python.org/library/struct.html

From: johnty on 2 Jun 2010 03:32
On Jun 2, 12:04 am, Christian Heimes <li...(a)cheimes.de> wrote:
> > i'm reading bytes from a serial port, and storing it into an array.
>
> > each byte represents a signed 8-bit int.
>
> > currently, the code i'm looking at converts them to an unsigned int by
> > doing ord(array[i]). however, what i'd like is to get the _signed_
> > integer value. whats the easiest way to do this?
>
> http://docs.python.org/library/struct.html

the struct docs is exactly what i needed to read. "unpacking" it as a
signed char did the trick. thanks guys!
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