Boost.Python: using C++ get/set methods to provide Python attributes

From: Jeff Johnson 44644 (jjphatt_at_[hidden])
Date: 2001-05-02 15:03:21

Howdy folks,

Has anyone thought about supporting the use of C++ get()
and set() methods to define Python attributes?  Some other
Python/C++ tools allow you to do this, and it's really
helpful.

For example:

A C++ class representing an ideal gas in a reservoir:

class Gas {
   public:

   ...

   // Get the temperature of the gas.  
   double getTemperature() const;

   // Set the temperature of the gas.  
   void setTemperature(double newTemperature);

   // Get the pressure of the gas.  
   double getPressure() const;

   // Set the pressure of the gas.  
   void setPressure(double newPressure);

   // Get the volume in which the gas is contained.
   double getVolume() const;

   // Set the size of the reservoir containing the gas.
   void setVolume(double newVolume);

};

may correspond to a Python class with attributes
temperature, pressure, and volume.  There's no need, per
se, for us to impose the C++ notion of get()ting and
set()ting attributes if we can just make the get() and
set() functions transparent within Boost.Python.

For example, here's the way we currently have to do
things:

>>> from Gas import * 
>>> gas = Gas() 
>>> gas.setVolume(20.0); 
>>> gas.setTemperature(298.0); 
>>> gas.setPressure(1.0); 
>>> gas.getTemperature() 
298.0 

It seems to me we could easily add functionality to
Boost.Python that would make it possible to do this:

>>> from Gas import * 
>>> gas = Gas() 
>>> gas.volume = 20.0          # Calls C++ setVolume(20.0) 
>>> gas.temperature = 298.0    # Calls C++ setTemperature(298.0) 
>>> gas.pressure = 1.0         # Calls C++ setPressure(1.0) 
>>> gas.temperature            # Calls C++ getTemperature() 298.0

I work on a scientific code that uses python as a
front-end to C++, and the package we currently use to map
C++ classes into Python supports this functionality, but
we would really like to start using Boost.  If I can
provide a way for Boost to do this, is there any interest
in this sort of thing?

(BTW, this can be extended to support "read-only" Python
attributes, which have been discussed here before.  To
make a read-only Python attribute, you would simply
associate the attribute with a given C++ get() function
and skip the set() function.)

Thanks, 
Jeffrey Johnson