[C++-sig] Bugs in the Boost.Python tutorial example

[Raghvendra Jain]

Hi Michael,

I had written a tutorial on Compiling Boost.Python using Visual Studio.
Please check.

http://www.sigverse.org/wiki/en/index.php?Compiling%20Boost.Python%20for%20Python%20in%20Visual%20Studio

I know I am not directly answering the questions you raised here, but I
guess it might help you since this method is working for me and several
others.
My aim was to embed Python inside the C++ code, so that I can call Python
functions. I guess your aim is to call C++ functions from Python.
Nevertheless, the process of building the example, is not so different.
Please let me know if it helps.

I am running on a deadline, else I would have tried to find a concrete
solution to your issues. Sorry again.

Cheers,
Raghav

On Mon, Nov 17, 2014 at 1:10 PM, Michael Rolle <m at rolle.name> wrote:

>  Hi,
>
> I had a hard time building the example/tutorial project.  Some of this is,
> I believe, due to bugs in the distribution, and some is probably my lack of
> understanding.
>
> Some of this I posted to the Boost interest group before I could join this
> (Python C++) SIG, hoping it would get forwarded on here, so there may be a
> duplication.
>
> 1. Calling bjam in the example/tutorial project failed to even start up
> the build system.  This was because the example/bootstrap.jam pointed to
> the wrong path for the build system root.  Instead of
> ../../../tools/build/v2, it should be ../../../tools/build/src/kernel.
> When I changed this, bjam now got past the build system startup.
>
> 2. Building the project not only compiles hello.cpp, but it also builds a
> private copy of the Boost/Python library.  So I needed to supply the
> properties needed to correctly build this library (i.e., link=shared,
> address-mode=64).  Of course, I needed to supply those same properties
> anyway as part of creating the extension.
>
> There's probably a way to change something so that the extension uses the
> library built in the Boost.Python's own project, or if I have obtained the
> libraries without having to build them, it would use these.  I don't know
> if you intended to have the tutorial example make its own copies, but it
> seems a waste of resources to do so.
>
> 3. The link for debug mode failed, saying that the .pdb file was in the
> wrong format (LNK1207).  This is a bug, due to an option in the link
> command '/IMPORTLIB:...hello_ext.pdb'.  So the linker is creating the .pdb
> file as an import library, then complaining that it's not a valid pdb
> file.  I changed '.pdb' to '.lib'.  I could also have removed this option
> entirely, since hello_ext.pyd doesn't have anything to export anyway.
>
> 4. Before figuring out that the link was the problem, I changed the /Z7
> argument to /Zi in the compile command for hello.cpp.  I don't know if this
> was necessary, or if it was necessary to leave it in place.  For now, I
> just wanted to get it to build.  Without /Z7, the debug symbols go into
> example/tutorial/vc120.pdb.  I don't know if the linker found these or
> not.  When I try stepping into the extension, I'll know for sure.
> Microsoft prefers that .pdb files be used for debug symbols rather than
> embedding them in the .obj files, so this might be the only real reason to
> make the change.
>
> 4. The link for both release mode failed with two undefined symbols,
> __imp_DecodePointer and __imp_EncodePointer, which are in kernel32.lib.  I
> tried adding kernel32.lib to the link's inputs.  But then it warned that
> there could be static constructors/destructors not getting called.  After
> much research on this topic, I found that the source of the problem was the
> /NOENTRY argument in the link command, which has the consequence that the
> automatic CRT initialization of the DLL doesn't occur.  So I remove the
> /NOENTRY and got not warnings, and I didn't need to add kernerl32.lib
> either.
>
> 5. A minor point.  The MACHINE:X64 is redundant.  The linker knows it's
> X64 because of the architecture of the input files and libraries.  Nothing
> wrong with it being there, but it's just clutter in the code.
>
> 6. Now bjam was successful in building whatever it wanted to build.  It
> said that hello.test passed.  Sounds great, I thought.  But I then went
> into Python and tried 'import hello_ext' and that failed.  So I have an
> issue with the test program passing, while the extension didn't actually
> work.
>
> 7. The problem was that bjam didn't put the hello_ext.pyd file in my
> Python's lib/site-packages folder.  It built the .pyd and .pdb files in the
> example/tutorial/bin/... staging area, and copied (ONLY) the .pyd file to
> example/tutorial.  So not only did the .pyd file get put in the wrong
> place, but the .pdb was left out.  If I am going to debug my extension
> (such as with Visual Studio's Python Tools), the .pdb file also needs to be
> in the lib/site-packages folder.  Without the .pdb file, the PTVS debugger
> will not set breakpoints or step into the extension code.
>
> To summarize, the fixes I made in order to build the example and use it in
> Python were:
>     * Change the build system path in examples/bootstrap.jam.
>     * Change the /IMPORTLIB:....pdb to ....lib in the link command.  I
> could have removed it altogether.
>     * Remove /NOENTRY from the link command.
>     * Manually copy the example/tutorial/bin/.../hello_ext.(pyd,pdb) files
> to Python's lib/site-packages.
>
> This cost me about a whole day's time, and I'm pretty resourceful.  And I
> actually want to build my own extensions in VS instead of bjam, linking to
> the Boost.Python DLL.  I started of by trying this, and my extension
> crashed.  So that's why I went about building the example with bjam, to at
> least see what a successful deployment looked like.  But I'll still have to
> figure out what went wrong with my original attempt; there may be
> additional bugs to report.
>
> I suppose that a lot of people would have given up building the tutorial
> example and then given up on Boost.Python altogether.
>
> Michael Rolle
> (408) 313-8149
>
> _______________________________________________
> Cplusplus-sig mailing list
> Cplusplus-sig at python.org
> https://mail.python.org/mailman/listinfo/cplusplus-sig
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/cplusplus-sig/attachments/20141117/07c9b462/attachment-0001.html>