ctypes integration


Boost.Python is really a very powerful library, but if you are working with code written in plain “C” - you’ve got a problem. You have to create wrappers for almost every function or variable.

In general, if you want to work with plain “C” code from Python you don’t have to create any wrapper - you can use ctypes package.

About ctypes

ctypes is a foreign function library for Python. It provides C compatible data types, and allows one to call functions in dlls/shared libraries. It can be used to wrap these libraries in pure Python.

The idea

The idea behind “ctypes integration” functionality is really simple: you configure Py++ to expose address of the variable\return value, and than you you use ctypes from_address functionality to access and modify the data.

Obviously, this approach has pros and cons:

  • cons - it could be very dangerous - you can corrupt your application memory
  • cons - managing memory is not something a typical Python user get used to. It is too “low level”.
  • pros - you don’t need to create wrapper in C++
  • pros - a Python user has access to the data
  • pros - compilation time is smaller
  • pros - you still can create wrapper, but using Python

In my opinion, the better way to go is to “mix”:

  1. expose your native code using Boost.Python and “ctypes integration” functionality - it is easy and cheap
  2. use ctypes module to access your data
  3. create high level API in Python: the wrappers, which will ensure the constraints and will provide more “natural” interface

Implemented functionality

Py++ is able to

  • expose global and member variable address
  • expose “this” pointer value
  • expose a class “sizeof”
  • expose variable, which has a union type
  • return address of return value as integer - new call policy was created

Future directions

The functionality is going to be developed father and I intend to add the following features:

  • to port this functionality to 64bit systems
  • to add ability to expose “C” functions without using Boost.Python.