| Python and IDL [message #39570] |
Fri, 28 May 2004 08:38  |
Michael Wallace
Messages: 409
Registered: December 2003
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Senior Member |
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I'm probably the only person here who'd be interested in this, but I
guess I'll throw it out anyway.
I have recently started using Python and love the language. Python is
interpreted, interactive, object oriented, and has dynamic data types
and dynamic typing. From this perspective, IDL and Python are very
similar. There are even projects such as SciPy (http://www.scipy.org)
which add some scientific analysis to the language.
Python does have a couple nice benefits, namely the huge number of
modules available where there's everything from operating system
commands to networking to XML to email etc. One thing I've found myself
doing recently is writing my core analysis processing code in IDL and
then writing a Python wrapper around the particular code. For example,
in one of my programs, I use Python to automatically download files from
an FTP site and then call IDL to do the specific processing on the
files. In another program, I use Python to process command line
arguments and then call the appropriate IDL code based on the arguments.
Currently, in my Python programs I open a pipe to an IDL process and
write the IDL commands to the pipe. What I'm wondering is if there is
an efficient way to send data from IDL back to Python. The only thing
I've found so far is to have IDL write data to stdout and set up the
Python side to read this stream. However, this can get pretty
inefficient at times. Without any direct conversion between the two
languages available, are there any other (i.e. better, efficient) ways
to set up bi-directional interprocess communication between Python and IDL?
What'd be really nice is if RSI provided some mechanism for IDL and
Python to communicate at a much closer level than interprocess
communication. Karl, that's a hint. ;-)
-Mike
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| Re: Python and IDL [message #39612 is a reply to message #39570] |
Fri, 04 June 2004 10:54  |
Bob[2]
Messages: 5
Registered: June 2004
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Junior Member |
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Michael Wallace wrote:
>
> What'd be really nice is if RSI provided some mechanism for IDL and
> Python to communicate at a much closer level than interprocess
> communication. Karl, that's a hint. ;-)
Michael, take a look at "External Development Guide" in the IDL help
documentation, especially the first chapter. They guide you through the
intricacies, e.g., p.13:
--
Supported Inter-Language Communication Techniques in IDL
IDL supports a number of different techniques for communicating with the
operating system and programs written in other languages. These methods
are described, in brief, below.
Options are presented in approximate order of increasing complexity. We
recommend that you favor the simpler options at the head of this list
over the more complex ones that follow if they are capable of solving
your problem.
--
-Bob
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| Re: Python and IDL [message #39619 is a reply to message #39570] |
Fri, 04 June 2004 03:13 |
Nigel Wade
Messages: 286
Registered: March 1998
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Senior Member |
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On Fri, 28 May 2004 10:38:08 -0500, Michael Wallace wrote:
> I'm probably the only person here who'd be interested in this, but I
> guess I'll throw it out anyway.
>
> I have recently started using Python and love the language. Python is
> interpreted, interactive, object oriented, and has dynamic data types
> and dynamic typing. From this perspective, IDL and Python are very
> similar. There are even projects such as SciPy (http://www.scipy.org)
> which add some scientific analysis to the language.
>
> Python does have a couple nice benefits, namely the huge number of
> modules available where there's everything from operating system
> commands to networking to XML to email etc. One thing I've found myself
> doing recently is writing my core analysis processing code in IDL and
> then writing a Python wrapper around the particular code. For example,
> in one of my programs, I use Python to automatically download files from
> an FTP site and then call IDL to do the specific processing on the
> files. In another program, I use Python to process command line
> arguments and then call the appropriate IDL code based on the arguments.
>
> Currently, in my Python programs I open a pipe to an IDL process and
> write the IDL commands to the pipe. What I'm wondering is if there is
> an efficient way to send data from IDL back to Python. The only thing
> I've found so far is to have IDL write data to stdout and set up the
> Python side to read this stream. However, this can get pretty
> inefficient at times. Without any direct conversion between the two
> languages available, are there any other (i.e. better, efficient) ways
> to set up bi-directional interprocess communication between Python and IDL?
>
> What'd be really nice is if RSI provided some mechanism for IDL and
> Python to communicate at a much closer level than interprocess
> communication. Karl, that's a hint. ;-)
>
> -Mike
The cleanest way would be to create a Python DLM, built using
an embedded Python interpreter. The DLM interface routines could pick
apart any IDL variables and create Python variables (possibly) using the
same memory (you'd need to check on row-major vs. column-major issues for
multi-dimensional arrays), then add these Python variables to the global
dictionary.
I've built an embedded interpreter into a C program, but not an IDL
DLM. I don't think there are any intrinsic reasons why it wouldn't be
possible.
--
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555
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| Re: Python and IDL [message #39631 is a reply to message #39570] |
Thu, 03 June 2004 06:21 |
Stein Vidar Hagfors H[2]
Messages: 28
Registered: October 2002
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Junior Member |
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Michael Wallace <mwallace.no.spam@no.spam.swri.edu.invalid> writes:
> I'm probably the only person here who'd be interested in this, but I
> guess I'll throw it out anyway.
Well, you're not quite alone ;-)
[...]
> Currently, in my Python programs I open a pipe to an IDL process and
> write the IDL commands to the pipe. What I'm wondering is if there is
> an efficient way to send data from IDL back to Python. The only thing
> I've found so far is to have IDL write data to stdout and set up the
> Python side to read this stream. However, this can get pretty
> inefficient at times. Without any direct conversion between the two
> languages available, are there any other (i.e. better, efficient) ways
> to set up bi-directional interprocess communication between Python and
> IDL?
My advice would be to use remote procedure calls (RPC) from python to
an instance of IDL running as an RPC server. It would need some
development of wrapper routines callable from python (written in
c). For the IDL side of it, look at the files in
$IDL_DIR/external/rpc/. The example.c is a bare-bones example of how
to connect & send command lines to IDL. Look at e.g. idl_rpc_test.c to
see examples of how to use the numerous features.
With RPC calls, you can set or get variables "directly". For even more
efficiency, one could even build IDL & python together using Callable
IDL.
> What'd be really nice is if RSI provided some mechanism for IDL and
> Python to communicate at a much closer level than interprocess
> communication. Karl, that's a hint. ;-)
It would be nice, yes. Due to the large body of legacy code that many
projects around here are relying on, the likelihood of switching
entirely to python is very small. But a number of people would prefer
using python for the "scripting" parts of a data processing pipeline.
--
------------------------------------------------------------ --------------
Stein Vidar Hagfors Haugan
ESA SOHO SOC/European Space Agency Science Operations Coordinator for SOHO
NASA Goddard Space Flight Center, Tel.: 1-301-286-9028
Mail Code 682.3, Bld. 26, Room G-1, Cell: 1-240-354-6066
Greenbelt, Maryland 20771, USA. Fax: 1-301-286-0264
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| Re: Python and IDL [message #39646 is a reply to message #39570] |
Wed, 02 June 2004 08:55 |
idl_toolmaker
Messages: 1
Registered: June 2004
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Junior Member |
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Michael Wallace <mwallace.no.spam@no.spam.swri.edu.invalid> wrote in message news:
>
> Currently, in my Python programs I open a pipe to an IDL process and
> write the IDL commands to the pipe. What I'm wondering is if there is
> an efficient way to send data from IDL back to Python.
Does Python pass data by reference, like IDL? You can work with
pointers to your data structure, maybe.
- Bob
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