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From: jjphatt_at_[hidden]
Date: 2001-05-02 12:21:07

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


   // 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()

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()

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.)

Jeffrey Johnson

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