[PyQt] Running Python scripts from a SIP-wrapped library

Jens Thoms Toerring jt at toerring.de
Sat Jul 30 21:33:55 BST 2011


   I guess this isn't the best place to ask but I haven't
found anything really fitting yet. So, please, if this is
too off-topic don't hesitate to redirect me to a better
place (a "RTFM" is also going to be appreciated as long
as it comes with a pointer to the relevant "M";-).

In short, I have a C++ library that has a SIP wrapper, so
it can be used from both Python and C++. Within the library
it should be possible to execute "modules", i.e. Python
scripts, using the Python C-API. Those "modules" also need
to 'import' the SIP-wrapper for the library.

I got this working using the following approach: In the
code that runs a Python "module" I check first if Python
is already running (that would be the case when the li-
brary is used from Python via the SIP-wrapper) by testing
with Py_IsInitialized(). If that isn't the case I call
PyInitialize(). On the other hand, when it's true I start
a new Python interpreter, using Py_NewInterpreter()
(creating a new interpreter seems to be necessary since
otherwise Python crashes somewhere in its innards with
a segmentation fault once I call PyImport_Import() on
the Python module to be executed). Once the "module" is
done I stop the new interpreter with Py_EndInterpreter()
(if one was started) or just call PyFinalize().

  All this seems to work fine when the Python script
using my library is started from the command line. But
now someone wanted to use spyder


And if the Python script is run from spyder all kinds of
weired things happen. In some cases the script simply seems
to hang (one place seems to be the call of Py_NewInterpre-
ter() as far as I can tell at the moment - I haven't found
a good way to run spyder under a debugger and then getting
at the place where things happen) or it aborts with one
of several error messages about 'tstate mixup' and similar
when the module has been run and the interpreter is removed.

I have been googling and trying to understand the docu-
mentation I found for several days now and am still com-
pletely confused. I haven't found some really coherent
description what all this stuff what the GIL and Thread-
States are all about and how far that could be at the
heart of my problems. The C-API reference documentation
is nice as far as it goes, but it's mainly a description
of a lot of functions with not enough background informa-
tion for me to help me figure out what actually is going

Perhaps someone with more knowledge about the details of
Python and interfacing with C/C++ can tell me either that
my whole approach is completely idiotic or, if it's not
that bad, can give me some hints where I'm going wrong
- or at least has some tips for things I should read and
try to understand...
                       Thanks and best regards, Jens
  \   Jens Thoms Toerring  ________      jt at toerring.de
   \_______________________________      http://toerring.de

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