# Boost.Python - <boost/python/data_members.hpp>

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# Boost.Python

## Header <boost/python/data_members.hpp>

## Contents

Introduction
Functions
  make_getter
  make_setter
Example

## Introduction

`make_getter()` and `make_setter()` are the functions used internally by `class_<>::def_readonly` and `class_<>::def_readwrite` to produce Python callable objects which wrap C++ data members.

## Functions

    template <class C, class D>
    objects::function* make_getter(D C::*pm);

    template <class C, class D, class Policies>
    objects::function* make_getter(D C::*pm, Policies const& policies);

Requires: `Policies` is a model of CallPolicies.
Effects: Creates a Python callable object which accepts a single argument that can be converted `from_python` to `C*`, and returns the corresponding member `D` member of the `C` object, converted `to_python`. If `policies` is supplied, it will be applied to the function as described here.
Returns: A pointer convertible to `PyObject*` which refers to the new Python callable object.

    template <class C, class D>
    objects::function* make_setter(D C::*pm);

    template <class C, class D, class Policies>
    objects::function* make_setter(D C::*pm, Policies const& policies);

Requires: `Policies` is a model of CallPolicies.
Effects: Creates a Python callable object which, when called from Python, expects two arguments which can be converted `from_python` to `C*` and `D const&`, respectively, and sets the corresponding `D` member of the `C` object. If `policies` is supplied, it will be applied to the function as described here.
Returns: A pointer convertible to `PyObject*` which refers to the new Python callable object.

## Example

The code below uses make_getter and make_setter to expose a data member as functions:

    #include <boost/python/data_members.hpp>
    #include <boost/python/module.hpp>
    #include <boost/python/class.hpp>

    struct X
    {
        X(int x) : y(x) {}
        int y;
    };

    using namespace boost::python;

    BOOST_PYTHON_MODULE_INIT(data_members_example)
    {
        module("data_members_example")
            .add(
                class_<X>("X")
                   .def_init(args<int>())
                   .def("get", make_getter(&X::y))
                   .def("set", make_setter(&X::y))
            )
            ;
    }

It can be used this way in Python:

    >>> from data_members_example import *
    >>> x = X(1)
    >>> x.get()
    1
    >>> x.set(2)
    >>> x.get()
    2

8 May 2002

© Copyright Dave Abrahams 2002. All Rights Reserved.