[C++-sig] Py++/boost::python: How to correctly wrap libraries (DLLs) with dependencies on each other.

[Martin Seiler]

Thanks a lot Roman, everything answered..

On Wed, Jan 20, 2010 at 9:22 AM, Roman Yakovenko
<roman.yakovenko at gmail.com> wrote:
> On Mon, Jan 11, 2010 at 6:15 PM, mtn <mtn at xcm.ch> wrote:
>>
>> Hi all,
>>
>> I try to embed a Python interpreter into my project using
>> Py++/boost::python.
>>
>> I have a problem wrapping different libraries for which i own the source and
>> which I compile to DLL/*.so files . The libraries have dependencies on each
>> other but do not necessarily have to be used together.
>>
>>
>> An abstract example:
>>
>> The interpreter is in a library on which all other libraries depend and
>> where they register themselves using init functions generated by
>> py++/boost::python.
>> Let's say I have a base library B.
>> Additionally a library E extending library B.
>>
>> lib B:
>> class __exported_to_python__ Base {
>>  void __exported_to_pytthon__  foo(){...}
>> }
>>
>> lib E -> depends B:
>> class __exported_to_python__ Extended : public B
>> {
>>  void __exported_to_python__  boo(){...}
>> }
>>
>> It makes sense to also use B alone, therefore I would like to build a Python
>> wrapper for each library directly into the DLL.
>>
>> Now I register my init function generate by Py++/boost::python to the
>> interpreter instance using `PyImport_AppendInittab`.
>>
>> The thing, that I cannot generate a proper inheritance relation between the
>> class `Extended` and `Base` without telling Py++ to wrap both classes. But
>> then I have wrapped `Base` twice. Once in B and once in E.
>> And when boost::python tries to register some transfer functions based on
>> the C++ type (RTTI) it fails, as it has already been registered (because
>> init_B was called).
>>
>> If I simply delete the duplicated classes by hand from the wrapper of
>> library `E` it works.
>> But one has to ensure that first `B` is imported to Python (`import B`) and
>> afterwards `E` (`import E`) otherwise boost::python does not have `Base`
>> registered on which `Extended` depends.
>
> You can import "B" from "E". You can do this by building "EImpl"
> module and the "wrapping" it with package:
>  E/
>     __init__.py
>     EImpl.[so|pyd|dll]
>
> where __init__.py contains the following code:
>
> import B
> from EImpl import * #or something like that
>
>
>>
>> I hope I made myself clear enough now :-)
>> So has anybody solved this problem before me?
>> I did not find a source which would explain how to solve this issue with
>> Py++ and boost::python.
>
> Take a look on http://language-binding.net/pyplusplus/documentation/multi_module_development.html
> . The document describes the situation you have.
>
> If you need a good example take a look on Python-Ogre project. It uses
> "multi module development" feature all the way.
>
> HTH
>
> --
> Roman Yakovenko
> C++ Python language binding
> http://www.language-binding.net/
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