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97 lines
4.4 KiB
ReStructuredText
97 lines
4.4 KiB
ReStructuredText
.. _extending-distutils:
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*******************
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Extending Distutils
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*******************
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Distutils can be extended in various ways. Most extensions take the form of new
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commands or replacements for existing commands. New commands may be written to
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support new types of platform-specific packaging, for example, while
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replacements for existing commands may be made to modify details of how the
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command operates on a package.
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Most extensions of the distutils are made within :file:`setup.py` scripts that
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want to modify existing commands; many simply add a few file extensions that
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should be copied into packages in addition to :file:`.py` files as a
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convenience.
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Most distutils command implementations are subclasses of the :class:`Command`
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class from :mod:`distutils.cmd`. New commands may directly inherit from
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:class:`Command`, while replacements often derive from :class:`Command`
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indirectly, directly subclassing the command they are replacing. Commands are
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required to derive from :class:`Command`.
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.. % \section{Extending existing commands}
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.. % \label{extend-existing}
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.. % \section{Writing new commands}
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.. % \label{new-commands}
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.. % \XXX{Would an uninstall command be a good example here?}
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Integrating new commands
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========================
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There are different ways to integrate new command implementations into
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distutils. The most difficult is to lobby for the inclusion of the new features
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in distutils itself, and wait for (and require) a version of Python that
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provides that support. This is really hard for many reasons.
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The most common, and possibly the most reasonable for most needs, is to include
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the new implementations with your :file:`setup.py` script, and cause the
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:func:`distutils.core.setup` function use them::
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from distutils.command.build_py import build_py as _build_py
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from distutils.core import setup
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class build_py(_build_py):
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"""Specialized Python source builder."""
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# implement whatever needs to be different...
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setup(cmdclass={'build_py': build_py},
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...)
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This approach is most valuable if the new implementations must be used to use a
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particular package, as everyone interested in the package will need to have the
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new command implementation.
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Beginning with Python 2.4, a third option is available, intended to allow new
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commands to be added which can support existing :file:`setup.py` scripts without
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requiring modifications to the Python installation. This is expected to allow
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third-party extensions to provide support for additional packaging systems, but
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the commands can be used for anything distutils commands can be used for. A new
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configuration option, :option:`command_packages` (command-line option
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:option:`--command-packages`), can be used to specify additional packages to be
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searched for modules implementing commands. Like all distutils options, this
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can be specified on the command line or in a configuration file. This option
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can only be set in the ``[global]`` section of a configuration file, or before
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any commands on the command line. If set in a configuration file, it can be
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overridden from the command line; setting it to an empty string on the command
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line causes the default to be used. This should never be set in a configuration
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file provided with a package.
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This new option can be used to add any number of packages to the list of
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packages searched for command implementations; multiple package names should be
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separated by commas. When not specified, the search is only performed in the
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:mod:`distutils.command` package. When :file:`setup.py` is run with the option
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:option:`--command-packages` :option:`distcmds,buildcmds`, however, the packages
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:mod:`distutils.command`, :mod:`distcmds`, and :mod:`buildcmds` will be searched
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in that order. New commands are expected to be implemented in modules of the
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same name as the command by classes sharing the same name. Given the example
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command line option above, the command :command:`bdist_openpkg` could be
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implemented by the class :class:`distcmds.bdist_openpkg.bdist_openpkg` or
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:class:`buildcmds.bdist_openpkg.bdist_openpkg`.
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Adding new distribution types
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=============================
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Commands that create distributions (files in the :file:`dist/` directory) need
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to add ``(command, filename)`` pairs to ``self.distribution.dist_files`` so that
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:command:`upload` can upload it to PyPI. The *filename* in the pair contains no
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path information, only the name of the file itself. In dry-run mode, pairs
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should still be added to represent what would have been created.
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