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<title>8.1 Integrating new commands</title>
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<H1><A NAME="SECTION008100000000000000000">
8.1 Integrating new commands</A>
</H1>

<P>
There are different ways to integrate new command implementations into
distutils.  The most difficult is to lobby for the inclusion of the
new features in distutils itself, and wait for (and require) a version
of Python that provides that support.  This is really hard for many
reasons.

<P>
The most common, and possibly the most reasonable for most needs, is
to include the new implementations with your <span class="file">setup.py</span> script,
and cause the <tt class="function">distutils.core.setup()</tt> function use them:

<P>
<div class="verbatim"><pre>
from distutils.command.build_py import build_py as _build_py
from distutils.core import setup

class build_py(_build_py):
    """Specialized Python source builder."""

    # implement whatever needs to be different...

setup(cmdclass={'build_py': build_py},
      ...)
</pre></div>

<P>
This approach is most valuable if the new implementations must be used
to use a particular package, as everyone interested in the package
will need to have the new command implementation.

<P>
Beginning with Python 2.4, a third option is available, intended to
allow new commands to be added which can support existing
<span class="file">setup.py</span> scripts without requiring modifications to the Python
installation.  This is expected to allow third-party extensions to
provide support for additional packaging systems, but the commands can
be used for anything distutils commands can be used for.  A new
configuration option, <span class="du-option">command_packages</span> (command-line option
<b class="programopt">--command-packages</b>), can be used to specify additional
packages to be searched for modules implementing commands.  Like all
distutils options, this can be specified on the command line or in a
configuration file.  This option can only be set in the
<code>[global]</code> section of a configuration file, or before any
commands on the command line.  If set in a configuration file, it can
be overridden from the command line; setting it to an empty string on
the command line causes the default to be used.  This should never be
set in a configuration file provided with a package.

<P>
This new option can be used to add any number of packages to the list
of packages searched for command implementations; multiple package
names should be separated by commas.  When not specified, the search
is only performed in the <tt class="module">distutils.command</tt> package.  When
<span class="file">setup.py</span> is run with the option
<b class="programopt">--command-packages</b> <b class="programopt">distcmds,buildcmds</b>,
however, the packages <tt class="module">distutils.command</tt>, <tt class="module">distcmds</tt>,
and <tt class="module">buildcmds</tt> will be searched in that order.  New commands
are expected to be implemented in modules of the same name as the
command by classes sharing the same name.  Given the example command
line option above, the command <code class="du-command">bdist_openpkg</code> could be
implemented by the class <tt class="class">distcmds.bdist_openpkg.bdist_openpkg</tt>
or <tt class="class">buildcmds.bdist_openpkg.bdist_openpkg</tt>.

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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