[Boost-users] [python] a lot of hassle getting started with embedding and vc8

From: Markus Werle (numerical.simulation_at_[hidden])
Date: 2008-08-11 08:19:19

Hi folks!

Probably someone with some hints on how to fix this.
I may have overlooked portions of the doc ...

Status: 
boost_1_36_beta installed using bjam for vc8/SP1 against python-2.5.2;
python test suite shows no failure. 

Trying to embed boost::python/Python in a Visual Studio 2008 project:
I managed to compile some code in debug mode (linking to python25.lib  
release mode). The embedded python interpreter (using the precompiled
version of python-2.5.2) throws an exception even on statements like "a=2", 
having "error_already_set", but PyErr_Print(); does not show a message, 
neither in Debugger nor after calling the executable from the command line. 

This is odd.
So it is time for a debug session - which is where true trouble begins:
fetch python source code, compile with vc8 in order to create python25_d.lib
and friends. 

Now what I really want is a *debug* executable with *statically* linked python 
and boost_python, so I tell it to the boost library 
by defining BOOST_DEBUG_PYTHON and BOOST_PYTHON_STATIC_LIB.

Defining BOOST_PYTHON_STATIC_LIB is necessary to have auto linker link to
the static boost_python libs (libboost_python-vc80-mt-sgd.lib)
[see http://thread.gmane.org/gmane.comp.lib.boost.user/38461/focus=38600]
but has a nasty side effect: 
Now the compiler decides python_25.lib has to be linked to rather than 
python25_w.lib. OUCH!

I digged into all headers (also using find/grep) to figure out why 
boost::python now thinks that python25.lib has to be linked into the executable,
but could not find the autolinker part for python*.lib.

The key part is in boost/python/detail/config.hpp, line 68

// backwards compatibility:
#ifdef BOOST_PYTHON_STATIC_LIB
#  define BOOST_PYTHON_STATIC_LINK
# elif !defined(BOOST_PYTHON_DYNAMIC_LIB)
#  define BOOST_PYTHON_DYNAMIC_LIB
#endif

I feel uncomfortable about the "backwards compatibility" tag in the comment.
So there must be some other way to get around this mess.

It all comes down to hinder BOOST_PYTHON_DYNAMIC_LIB to be defined.
 
Looking at [BINARY_DIST]python-2.5.2\include\pyconfig.h - a hand-written
version of the python config stuff, there might be some issue with 
with the "pragma comment(lib" portion ...

==================================================

OK, let us revert to dynamic linking then:

Using the code from example/quickstart/embedding.cpp I get a
<cite>
Unhandled exception at 0x00000000 in TestBoostPythonEmbedding.exe: 0xC0000005: 
Access violation reading location 0x00000000.
</cite>

triggered by 
python::object main = python::import("__main__");
calling
(*) python::handle<> module(PyImport_ImportModule(n)); // BOOM!

but calling PyImport_ImportModule("__main__"); directly succeeds.

but stepping into PyImport_ImportModule(n) fails.
What's wrong with (*) ?

The same game runs without error (!!!!) in release mode.

To be honest: I am lost. Any help or hint appreciated.

 
Markus