Is there a way to generate a c++ class from a python class and bind it a compile time?

Question

Is there a way to generate a relatively clean c++ class from a python class and bind it at compile-time?

For instance, if I have this python class:

class CarDef:
    acceleration = 1000.0
    brake = 1500.0
    inertia = acceleration * 0.1 * brake

    def __init__(self):
        pass

I'd like to have the corresponding c++ class:

class CarDef
{
public:
  double acceleration;
  double brake;
  double inertia;
  CarDef() 
  : acceleration( 1000.0 )
  , brake( 1500.0 )
  , inertia ( 150000.0 )
  {};
};

The resulting c++ class could be different, as well as the original python class: I could use a "getter methods" paradigm instead of class attributes.

What I'm trying to achieve is to create resource files in python that I'll be able to use in my c++ application. The goal is to reduce as much as possible the amount of code the end-user will have to write to add and use parameters; and it must avoid string comparison during the "running phase" (it's allowed during the "initialization phase").

I'd like the user to have to enter the resource name only twice: once in the python class, and once in the place where the resource will be used in the c++, assuming that the "magic" is going to bind the two items (either at run-time (which I doubt could be done without string comparison) or at compile time (an in-between step generates c++ class before the project is compiled)). This is why I'm going from python to c++; I believe that going from c++ to python would require at least 2 python files: one that is generated and one that inherits from the latter (to avoid overwriting already specified resources).

The end-user use would look like this:

// A singleton definition manager
class DefManager
{
  CarDef mCarDef;
public:
  static DefManager& GetReference() 
  {
    static DefManager instance;
    return instance;
  }

  CarDef& getCarDef() { return mCarDef; }
};

// One would use the generated CarDef class like this:
mCar.setSpeed( mCar.getSpeed() +  DefManager.GetReference().getCarDef().acceleration );

With this in mind, the python code is strictly outside of the c++ code.

One obvious problem I see is how to know what type a python attribute or method returns. I've seen a bit of examples of Cython, and it's seems to be able to use types (which is great!), but I haven't seen any examples where it could do what I need. Also, c generated code seems to still need Python.h and thus the cpython api libraries when compiling.

Is there any ways I could achieve this? Are there better way to do it?

• I'm using python 3.2+.
• I'm using MS Visual Studio 2010 (we plan to upgrade to 2013 soon).
• I'm on a 32 bit system (but we plan to upgrade to 64 bit soon, OS and developed software).

Answer 1

There is a way to go from C++ to Python but I do not know of any way of going from Python to C++. If you don't mind writing your code in C++ first, you can use the tool SWIG to auto generated for you Python classes.

Do note there are a few limitations around exception handling. You can set up to have your Python code throw C++ exceptions but the type of exception can be lost in translation. You also need to pay attention to handling of reference counted objects. SWIG will generate reference counting for Python which can sometimes delete objects unexpectedly.

If you don't like using a tool such as SWIG, there is also Boost.Python for C++. Again, this is C++ for Python bindings and does not auto generate C++ from Python.