Experimental Physics and
Industrial Control System

Tim Mooney <[email protected]> · Wed, 30 Sep 2009 12:49:56 -0500

Matt Newville wrote:

Hi Noboru, Wang, John, Michael, all,

As I've said before, I would be happy to collaborate to come up with a
more uniform approach to using CA with Python.
I agree with Noboru that a two-tier approach is needed.  I'm not so
sure that a 'thin wrapper to all of ca' is crucial.

I also agree with Noboru, and with most of your reply.  However, I'm in
favor of a 'thin wrapper to all of ca', at least as a one part of the
interface.  One reason is that I don't know all of the things I might
ever have to do with Python/CA, and I wouldn't want to invest effort
learning, and building a code base around, an interface that might run
out of gas when I need to do something that wasn't anticipated.

For example, I don't see significant advantages to having all the C CA
types (DBR_SHORT, DBR_INT, DBR_LONG, etc) exposed to Python at all, as
Python does not distinguish these types, and the difference never
needs to be exposed to the Python programmer.

I wouldn't want to say "never".  If the data are going to end up in
Python variables, I'd agree that DBR_SHORT and DBR_INT, for example,
are unnecessary complications.  But if I had to read a very large
array of two-byte integers, and hand the array off to some other
code that expects an array of two-byte integers, I would need at
minimum some way of specifying that two-byte integers be sent.

--Matt Newville <newville at cars.uchicago.edu>

--
Tim Mooney ([email protected]) (630)252-5417
Beamline Controls & Data Acquisition Group
Advanced Photon Source, Argonne National Lab.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System