Integrate Python And C++

Question

I'm learning C++ because it's a very flexible language. But for internet things like Twitter, Facebook, Delicious and others, Python seems a much better solution.

Is it possible to integrate C++ and Python in the same project?

Answer 1

Interfacing Python with C/C++ is not an easy task.

Here I copy/paste a previous answer on a previous question for the different methods to write a python extension. Featuring Boost.Python, SWIG, Pybindgen...

• You can write an extension yourself in C or C++ with the Python C-API.

  In a word: don't do that except for learning how to do it. It's very difficult to do it correctly. You will have to increment and decrement references by hand and write a lot of code just to expose one function, with very few benefits.

• Swig:

  pro: you can generate bindings for many scripting languages.

  cons: I don't like the way the parser works. I don't know if they've made some progress but two years ago the C++ parser was quite limited. Most of the time I had to copy/paste my .h headers to add some % characters and to give extra hints to the swig parser.

  I also needed to deal with the Python C-API from time to time for (not so) complicated type conversions.

  I'm not using it anymore.

• Boost.Python:

  pro: It's a very complete library. It allows you to do almost everything that is possible with the C-API, but in C++. I never had to write a C-API code with this library. I also never encountered a bug due to the library. Code for bindings either works like a charm or refuses to compile.

  It's probably one of the best solutions currently available if you already have some C++ library to bind. But if you only have a small C function to rewrite, I would probably try with Cython.

  cons: if you don't have a precompiled Boost.Python library you're going to use Bjam (sort of a replacement of make). I really hate Bjam and its syntax.

  Python libraries created with B.P tend to become obese. It also takes a lot of time to compile them.

• Py++: it's Boost.Python made easy. Py++ uses a C++ parser to read your code and then generates Boost.Python code automatically. You also have a great support from its author (no it's not me ;-) ).

  cons: only the problems due to Boost.Python itself.

  Edit this project looks discontinued. While probably still working it may be better to consider switching.

• Pybindgen:

  It generates the code dealing with the C-API. You can either describe functions and classes in a Python file, or let Pybindgen read your headers and generate bindings automatically (for this it uses pygccxml, a python library wrote by the author of Py++).

  cons: it's a young project, with a smaller team than Boost.Python. There are still some limitations: you cannot expose your own C++ exceptions, you cannot use multiple inheritance for your C++ classes.

  Anyway it's worth trying!

• Pyrex and Cython:

  Here you don't write real C/C++ but a mix between Python and C. This intermediate code will generate a regular Python module.

Edit Jul 22 2013: Now Py++ looks discontinued, I'm now looking for a good alternative. I'm currently experimenting with Cython for my C++ library. This language is a mix between Python and C. Within a Cython function you can use either Python or C/C++ entities (functions, variables, objects, ...).

Cython is quite easy to learn, has very good performance, and you can even avoid C/C++ completely if you don't have to interface legacy C++ libraries.

However for C++ it comes with some problems. It is less "automagic" than Py++ was, so it's probably better for stable C++ API (which is now the case of my library). The biggest problem I see with Cython is with C++ polymorphism. With Py++/boost:python I was able to define a virtual method in C++, override it in Python, and have the Python version called within C++. With Cython it's still doable but you need to explicitly use the C-Python API.

Edit 2017-10-06:

There is a new one, pybind11, similar to Boost.Python but with some potential advantages. For example it uses C++11 language features to make it simpler to create new bindings. Also it is a header-only library, so there is nothing to compile before using it, and no library to link.

I played with it a little bit and it was indeed quite simple and pleasant to use. My only fear is that like Boot.Python it could lead to long compilation time and large libraries. I haven't done any benchmark yet.