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.. Copyright David Abrahams 2006. Distributed under the Boost
.. Software License, Version 1.0. (See accompanying
.. file LICENSE_1_0.txt or copy at
.. http://www.boost.org/LICENSE_1_0.txt)

==============================================
 |(logo)|__ Boost.Python Build and Test HOWTO
==============================================

.. |(logo)| image:: ../../../boost.png
   :alt: Boost C++ Libraries:
   :class: boost-logo

__ ../index.html


.. section-numbering::
   :depth: 2

.. contents:: Contents
   :depth: 2
   :class: sidebar small

.. |newer| replace:: *newer*

Requirements
============

Boost.Python requires `Python 2.2`_ [#2.2]_ *or* |newer|__.  

.. _Python 2.2: http://www.python.org/2.2
__ http://www.python.org

Background
==========

There are two basic models for combining C++ and Python:

- extending_, in which the end-user launches the Python interpreter
  executable and imports Python “extension modules” written in C++.
  Think of taking a library written in C++ and giving it a Python
  interface so Python programmers can use it.  From Python, these
  modules look just like regular Python modules.

- embedding_, in which the end-user launches a program written
  in C++ that in turn invokes the Python interpreter as a library
  subroutine.  Think of adding scriptability to an existing
  application.

.. _extending: http://www.python.org/doc/current/ext/intro.html
.. _embedding: http://www.python.org/doc/current/ext/embedding.html

The key distinction between extending and embedding is the location
of the C++ ``main()`` function: in the Python interpreter executable,
or in some other program, respectively.  Note that even when
embedding Python in another program, `extension modules are often
the best way to make C/C++ functionality accessible to Python
code`__, so the use of extension modules is really at the heart of
both models.

__ http://www.python.org/doc/current/ext/extending-with-embedding.html

Except in rare cases, extension modules are built as
dynamically-loaded libraries with a single entry point, which means
you can change them without rebuilding either the other extension
modules or the executable containing ``main()``.

.. _quickstart:

No-Install Quickstart
=====================

There is no need to “install Boost” in order to get started using
Boost.Python.  These instructions use Boost.Build_ projects,
which will build those binaries as soon as they're needed.  Your
first tests may take a little longer while you wait for
Boost.Python to build, but doing things this way will save you from
worrying about build intricacies like which library binaries to use
for a specific compiler configuration and figuring out the right
compiler options to use yourself.

.. .. raw:: html

   <div style="width:50%">

.. Note:: Of course it's possible to use other build systems to
   build Boost.Python and its extensions, but they are not
   officially supported by Boost.  Moreover **99% of all “I can't
   build Boost.Python” problems come from trying to use another
   build system** without first following these instructions.

   If you want to use another system anyway, we suggest that you
   follow these instructions, and then invoke ``bjam`` with the

   .. parsed-literal::

     ``-a -o``\ *filename* 

   options to dump the build commands it executes to a file, so
   you can see what your alternate build system needs to do.

.. .. raw:: html
 
   </div>

.. _Boost.Build: ../../../tools/build/index.html

Basic Procedure
---------------

1. Get Boost; see sections 1 and 2 [`Unix/Linux`__, `Windows`__\ ] of the
   Boost `Getting Started Guide`_.

   __ ../../../more/getting_started/unix-variants.html#get-boost
   __ ../../../more/getting_started/windows.html#get-boost

2. Get the ``bjam`` build driver.  See section 5 [`Unix/Linux`__,
   `Windows`__\ ] of the Boost `Getting Started Guide`_.

   __ ../../../more/getting_started/unix-variants.html#prepare-to-use-a-boost-library-binary
   __ ../../../more/getting_started/windows.html#prepare-to-use-a-boost-library-binary


3. cd into the ``libs/python/example/quickstart/`` directory of your
   Boost installation, which contains a small example project.

4. Invoke ``bjam``.  Replace the “\ ``stage``\ “ argument from the
   example invocation from section 5 of the `Getting Started
   Guide`_ with “\ ``test``\ ,“ to build all the test targets.  Also add
   the argument “\ ``--verbose-test``\ ” to see the output generated by
   the tests when they are run.

   On Windows, your ``bjam`` invocation might look something like:

   .. parsed-literal::

     C:\\boost_1_34_0\\…\\quickstart> **bjam toolset=msvc --verbose-test test**

   and on Unix variants, perhaps,

   .. parsed-literal::

     ~/boost_1_34_0/…/quickstart$ **bjam toolset=gcc --verbose-test test**

.. Admonition:: Note to Windows Users

   For the sake of concision, the rest of this guide will use
   unix-style forward slashes in pathnames instead of the
   backslashes with which you may be more familiar.  The forward
   slashes should work everywhere except in `Command Prompt`_
   windows, where you should use backslashes.

   .. _Command Prompt: ../../../more/getting_started/windows.html#command-prompt

If you followed this procedure successfully, you will have built an
extension module called ``extending`` and tested it by running a
Python script called ``test_extending.py``.  You will also have
built and run a simple application called ``embedding`` that embeds
python.

.. _Getting Started Guide: ../../../more/getting_started/index.html

In Case of Trouble
------------------

If you're seeing lots of compiler and/or linker error messages,
it's probably because Boost.Build is having trouble finding your
Python installation.  You might want to pass the
``--debug-configuration`` option to ``bjam`` the first few times
you invoke it, to make sure that Boost.Build is correctly locating
all the parts of your Python installation.  If it isn't, consider
`Configuring Boost.Build`_ as detailed below.

If you're still having trouble, Someone on one of the following
mailing lists may be able to help:

* The `Boost.Build mailing list`__ for issues related to Boost.Build
* The Python `C++ Sig`__ for issues specifically related to Boost.Python

__ http://www.boost.org/more/mailing_lists.htm#jamboost
__ http://www.boost.org/more/mailing_lists.htm#cplussig

In Case Everything Seemed to Work
---------------------------------

Rejoice!  If you're new to Boost.Python, at this point it might be
a good idea to ignore build issues for a while and concentrate on
learning the library by going through the tutorial_ and perhaps
some of the `reference documentation`_, trying out what you've
learned about the API by modifying the quickstart project.

.. _reference documentation: v2/reference.html
.. _tutorial: tutorial/index.html

Modifying the Example Project
-----------------------------

If you're content to keep your extension module forever in one
source file called |extending.cpp|_, inside your Boost
distribution, and import it forever as ``extending``, then you can
stop here.  However, it's likely that you will want to make a few
changes.  There are a few things you can do without having to learn
Boost.Build_ in depth.

The project you just built is specified in two files in the current
directory: |boost-build.jam|_, which tells ``bjam`` where it can
find the interpreted code of the Boost build system, and
|Jamroot|_, which describes the targets you just built.  These
files are heavily commented, so they should be easy to modify.
Take care, however, to preserve whitespace.  Punctuation such as
``;`` will not be recognized as intended by ``bjam`` if it is not
surrounded by whitespace.

.. |boost-build.jam| replace:: ``boost-build.jam``
.. _boost-build.jam: ../example/quickstart/boost-build.jam

.. |Jamroot| replace:: ``Jamroot``
.. _Jamroot: ../example/quickstart/Jamroot

.. |extending.cpp| replace:: ``extending.cpp``
.. _extending.cpp: ../example/quickstart/extending.cpp

Relocate the Project
....................

You'll probably want to copy this project elsewhere so you can
change it without modifying your Boost distribution.  To do that,
simply

a. copy the entire ``libs/python/example/quickstart/`` directory
   into a new directory.

b. In the new copies of |boost-build.jam|_ and |Jamroot|_, locate
   the relative path near the top of the file that is clearly
   marked by a comment, and edit that path so that it refers to the
   same directory your Boost distribution as it referred to when
   the file was in its original location in the
   ``libs/python/example/quickstart/`` directory.

For example, if you moved the project from
``/home/dave/boost_1_34_0/libs/python/example/quickstart`` to
``/home/dave/my-project``, you could change the first path in
|boost-build.jam|_ from

.. parsed-literal::

  **../../../..**\ /tools/build/v2

to

.. parsed-literal::

  **/home/dave/boost_1_34_0**\ /tools/build/v2

and change the first path in |Jamroot|_ from

.. parsed-literal::

  **../../../..**

to

.. parsed-literal::

  **/home/dave/boost_1_34_0**

Add New or Change Names of Existing Source Files
................................................

The names of additional source files involved in building your
extension module or embedding application can be listed in
|Jamroot|_ right alongside ``extending.cpp`` or ``embedding.cpp``
respectively.  Just be sure to leave whitespace around each
filename::

  … file1.cpp file2.cpp file3.cpp …

Naturally, if you want to change the name of a source file you can
tell Boost.Build about it by editing the name in |Jamroot|_.

Change the Name of your Extension Module
........................................

The name of the extension module is determined by two things:

1. the name in |Jamroot|_ immediately following ``python-extension``, and 
2. the name passed to ``BOOST_PYTHON_MODULE`` in |extending.cpp|_.

To change the name of the extension module from ``extending`` to
``hello``, you'd edit |Jamroot|_, changing

.. parsed-literal::

  python-extension **extending** : extending.cpp ;

to

.. parsed-literal::

  python-extension **hello** : extending.cpp ;

and you'd edit extending.cpp, changing

.. parsed-literal::

  BOOST_PYTHON_MODULE(\ **extending**\ )

to

.. parsed-literal::

  BOOST_PYTHON_MODULE(\ **hello**\ )

Installing Boost.Python on your System
======================================

Since Boost.Python is a separately-compiled (as opposed to
`header-only`_) library, its user relies on the services of a
Boost.Python library binary.  

.. _header-only: ../../../more/getting_started/windows.html#header-only-libraries

If you need a regular installation of the Boost.Python library
binaries on your system, the Boost `Getting Started Guide`_ will
walk you through the steps of creating one.  If building binaries
from source, you might want to supply the ``--with-python``
argument to ``bjam`` (or the ``--with-libraries=python`` argument
to ``configure``), so only the Boost.Python binary will be built,
rather than all the Boost binaries.


Configuring Boost.Build
=======================

As described in the `Boost.Build reference manual`__, a file called
``user-config.jam`` in your home directory [#home-dir]_ is used to
specify the tools and libraries available to the build system. You
may need to create or edit ``user-config.jam`` to tell Boost.Build
how to invoke Python, ``#include`` its headers, and link with its
libraries.