Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of boost. Click here for the latest Boost documentation.

Boost.Python

Header <boost/python/exec.hpp>

Contents

Introduction
Functions
eval
exec
exec_file
Examples

Introduction

Exposes a mechanism for embedding the python interpreter into C++ code.

Functions

eval

object eval(str expression,
            object globals = object(),
            object locals = object());
Effects: Evaluate Python expression from expression in the context specified by the dictionaries globals and locals.
Returns: An instance of object which holds the value of the expression.

exec

object exec(str code,
            object globals = object(),
            object locals = object());
Effects: Execute Python source code from code in the context specified by the dictionaries globals and locals.
Returns: An instance of object which holds the result of executing the code.

exec_file

object exec_file(str filename,
                 object globals = object(),
                 object locals = object());
Effects: Execute Python source code from the file named by filename in the context specified by the dictionaries globals and locals.
Returns: An instance of object which holds the result of executing the code.

Examples

The following example demonstrates the use of import and exec to define a function in python, and later call it from within C++. 
#include <iostream>
#include <string>

using namespace boost::python;

void greet()
{ 
  // Retrieve the main module.
  object main = import("__main__");
  
  // Retrieve the main module's namespace
  object global(main.attr("__dict__"));

  // Define greet function in Python.
  object result = exec(
    "def greet():                   \n"
    "   return 'Hello from Python!' \n",
    global, global);

  // Create a reference to it.
  object greet = global["greet"];

  // Call it.
  std::string message = extract<std::string>(greet());
  std::cout << message << std::endl;
}
Instead of embedding the python script into a string, we could also store it in an a file... 
def greet():
   return 'Hello from Python!'
... and execute that instead. 
  // ...
  // Load the greet function from a file.
  object result = exec_file(script, global, global);
  // ...
}

Revised 01 November, 2005

© Copyright Stefan Seefeld 2005.