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File: SIDLPython.html
Copyright: (c) 2001 The Regents of the University of California
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Description: Basic documentation for Python.
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<h1>
Crash Course in SIDL's Python Mapping</h1>
<h2>
Tom Epperly <tepperly@llnl.gov><br />
Babel 0.8.x<br />
2 August 2001, updated 21 January 2003</h2>
<h3>
How to create a SIDL object in Python (once you've built the Python extension
module)</h3>
You need to import the extension module and then calling a method to create
an instance. If you have a class whose fully qualified name is
<tt>x.y.z</tt>,
you would say:
<pre>import x.y.z
obj = x.y.z.z()</pre>
The last part of the class name is repeated. The static methods of a class
are available in the Python <tt>x.y.z</tt> name space.
<p>In some cases, the Python extension module may be name
<tt>zmodule.so</tt>
instead of simply <tt>z.so</tt>. This might tempt you to say <tt>import
x.y.zmodule</tt> instead of just <tt>import x.y.z</tt>; resist this temptation!
<h3>
How to cast SIDL objects in Python</h3>
Let's say you have an object <tt>obj</tt>, and you would like to see if
it is an instance of a SIDL class or interface whose fully qualified name
is
<tt>x.y.z</tt>. This is how you do it.
<pre># assume obj already has its value
import x.y.z
zobj = x.y.z.z(obj)
if (zobj):
# now you've got a handle to a x.y.z object/interface
else:
# obj was not a handle to a x.y.z object/interface</pre>
Of course, you don't need the import if you know that <tt>x.y.z</tt> has
already been imported.
<h3>
Building Python Extension Modules</h3>
SIDL creates a <tt>Setup.in</tt> file that can be used to build the Python
extension modules that you create. Copy <tt>Makefile.pre.in</tt> from your
Python distribution into the directory containing
<tt>Setup.in</tt>. There
are three <tt>make</tt> variables you need to set when your building your
Python extension module.
<dl>
<dt>
SIDLLIBDIR</dt>
<dd>
This should be a path (absolute or relative) to the directory where the
SIDL runtime library file (i.e. the shared library/dynamic link library)
resides.</dd>
<dt>
SIDLPYHDRS</dt>
<dd>
This should be a path (absolute or relative) to the top directory in which
the basic SIDL Python extensions are installed.</dd>
<dt>
SIDLHDRS</dt>
<dd>
This should be a path (absolute or relative) to the directory where the
SIDL C header files are installed.</dd>
</dl>
Here is a hypothetical example:
<pre>make -f Makefile.pre.in SIDLLIBDIR=/usr/local/lib \
SIDLPYHDRS=/usr/local/include SIDLHDRS=/usr/local/include/SIDL
make SIDLLIBDIR=/usr/local/lib/libsidl.so \
SIDLPYHDR=/usr/local/include SIDLHDRS=/usr/local/include/SIDL</pre>
It is unlikely that any installation actually uses those settings.
<h3>
Setting up to run Python</h3>
Here I assume that you've installed BABEL in directories rooted at
<tt>${PREFIX}</tt>.
You need to have <tt>${PREFIX}/python</tt> in your
<tt>PYTHONPATH</tt>
environment variable in addition to the directory where you are doing your
work.
<p>On many systems, you will need <tt>${PREFIX}/lib</tt> in your
<tt>LD_LIBRARY_PATH</tt>
(or whatever system setting controls which directories are searched for
shared libraries/dynmic link libraries).
<p>You will likely need to use <tt>SIDL_DLL_PATH</tt> (a semicolon separated
path) to provide the path to the directory that holds the shared library/dynamic
link library containing the implementation of the SIDL objects.
<h3>
Notes</h3>
The Python binding for SIDL long is 32 bits instead of 64 bits at present.
<h3>
What does this error message mean?</h3>
<pre>>>> import x.y.Zmodule
Traceback (innermost last):
File "<stdin>", line 1, in ?
ImportError: dynamic module does not define init function (initZmodule)</pre>
Is the name of your SIDL interface/class <tt>x.y.Z</tt> or
<tt>x.y.Zmodule</tt>,
if it's the former, you should say <tt>import x.y.Z</tt>. If this isn't
the problem, submit a bug report for BABEL. It might be informative to
look at the symbol of the shared library/dynamic link library using a tool
like <tt>nm</tt>. I suppose it's also worth checking the <tt>PYTHONPATH</tt>
environment variable to make sure it's pointing to the right place.
<pre>>>> import x.y.Z
Fatal Python error: Cannot load implementation for SIDL class x.y.Z
Abort (core dumped)</pre>
This means that the Python stub code (the code that links Python to SIDL's
independent object representation (IOR)) failed in its attempt to load
the shared library or dynamic link library containing the implementation
of SIDL class <tt>x.y.Z</tt>. Make sure the environment variable
<tt>SIDL_DLL_PATH</tt>
lists all the directories where the shared libraries/dynamic link libraries
for your SIDL objects/interfaces are stored.
<tt>SIDL_DLL_PATH</tt> is
a <b>semicolon</b> separated list of directories where SIDL client stubs
will search for shared libraries required for SIDL classes and interfaces.
Make sure the directory in which the SIDL runtime resides is in the <tt>LD_LIBRARY_PATH</tt>
(or whatever your machine's mechanism for locating shared library files
is).
<pre>>>> import x.y.Z
Fatal Python error: Cannot load implementation for SIDL interface x.y.Z
Abort (core dumped)</pre>
This is the same problem for an interface as described immediately above
for a class.
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