ctypes integration¶

Introduction¶

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 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”:

expose your native code using Boost.Python and “ctypes integration” functionality - it is easy and cheap
use ctypes module to access your data
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