Cppyy – Automatic Python-C++ bindings | Hacker News Reader

Cppyy – Automatic Python-C++ bindings

cppyy.readthedocs.io

68 pointsd3k22 comments

How does this know the difference between:

  const char *cls::func(void)
  {
     return "abc"; // static: caller must not free
  }

and

  const char *cls::func(void)
  {
     return strdup("abc"); // caller must free
  }

Edit: I see: designed for large scale programs in high performance computing that use modern C++.

Modern C++ meaning, no pointers anywhere.

It looks like this gives you a `ctypes` pointer: https://cppyy.readthedocs.io/en/latest/basic_types.html#poin...

So you handle it like any other ctypes pointer, ie. `libc = ctypes.CDLL(find_library("c")); libc.free(ptr)`

Which is not fun in Python. So yeah, better avoid raw pointers.

There is also the less known https://github.com/google/clif (but not automatic)

From the comments below, it sounds like interfacing my C++ code with python using Cppyy would sacrifice performance.

Even so this will be awesome for unit testing. I really like the testing interface pytest provides, along with its parametrized tests.

Anyone else using python to test the logic their C/C++ code? I can't think of how I would test the memory allocation and freeing portion. Anyone think it's a bad idea?

The fuzz converting data types back and forth is probably not worth it.

But one can test the interface to the program nicely from python (i.e. text or socket i/o).

This is super interesting but if I am looking to bring C++ into my Python code base it would be because performance is important enough to do so. With that in mind I am not sure how this stacks up against compiled half steps like Cython or foreign function interfaces likes ctypes or CFFI instead.

If you have a Python code base and are looking to speed up some part of it, Cython is the way to go. Pybind11 and cppyy are more for cases where you have a bunch of C++ code that you want to provide a Python interface for.

Cython unfortunately doesn't have a very good pypy story, which cppyy does.

Check out the Rust python bindings too; specifically PyO3. If you're starting from scratch it's worth exploring. [1]

[1] https://www.benfrederickson.com/writing-python-extensions-in...

I need to create Python bindings for a C++ library and after a brief survey of the available options was planning on using SWIG (http://www.swig.org/tutorial.html). How does this compare?

SWIG is not always smooth to use, and you need to write interface files manually which in my experience are hard to debug. In Cppyy it looks like you don't have to do any of that.

Use pybind11 super easy to get startet with and reasonably easy to automate with libclang if your C++ API is simple.

Does anyone know of any well known tools that generate bindings in other languages e.g., Python from C++ code?

IIUC, this tool does the opposite i.e., generate C++/other language bindings from Python

The entirety of cpython’s runtime is exposed as a C api, so you can easily manipulate python objects in c or any language with a ffi. boost::python provides a c++ wrapper for cpython, which can be used to call both c/c++ in python and vice versa

> PyPy 5.7 and 5.8 have a built-in module cppyy.

Nice.

How does this compare to pybind11?

If you have a C++ project, you want to have Python bindings, and you don't want to share your header files, pybind11 is the way to go.

If you want to / can share your header files, cppyy is a very convenient way of being able to call your C++ code from Python. I'm not sure if there is a way to use it without headers.

One thing I wanted to do for a project at work is to add python bindings to our c++ library, having the least effort for having a decent python binding. Two features I am looking for are support for return values of custom objects of arbitrary size and c++ exceptions raising python exceptions. Cppyy seems to support these, do you know if/how they work on pybind11?

How do you link any cpp binary without headers without guessing the calling convention?

It's not so much that you never have the headers... more that you don't always want to provide the headers to everyone (since they may contain things you don't want to share.)

I looked into it a bit further, and cppyy does have provisions for this: https://cppyy.readthedocs.io/en/latest/bindings_generation.h...

I may have misread that page, but it looks like you can create a .rootmap and .pcm file and distribute that instead of the C++ headers.

Google PyInline

http://pyinline.sourceforge.net/

2001 vintage

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