1.. _extending-distutils: 2 3******************* 4Extending Distutils 5******************* 6 7Distutils can be extended in various ways. Most extensions take the form of new 8commands or replacements for existing commands. New commands may be written to 9support new types of platform-specific packaging, for example, while 10replacements for existing commands may be made to modify details of how the 11command operates on a package. 12 13Most extensions of the distutils are made within :file:`setup.py` scripts that 14want to modify existing commands; many simply add a few file extensions that 15should be copied into packages in addition to :file:`.py` files as a 16convenience. 17 18Most distutils command implementations are subclasses of the 19:class:`distutils.cmd.Command` class. New commands may directly inherit from 20:class:`Command`, while replacements often derive from :class:`Command` 21indirectly, directly subclassing the command they are replacing. Commands are 22required to derive from :class:`Command`. 23 24.. % \section{Extending existing commands} 25.. % \label{extend-existing} 26 27.. % \section{Writing new commands} 28.. % \label{new-commands} 29.. % \XXX{Would an uninstall command be a good example here?} 30 31 32Integrating new commands 33======================== 34 35There are different ways to integrate new command implementations into 36distutils. The most difficult is to lobby for the inclusion of the new features 37in distutils itself, and wait for (and require) a version of Python that 38provides that support. This is really hard for many reasons. 39 40The most common, and possibly the most reasonable for most needs, is to include 41the new implementations with your :file:`setup.py` script, and cause the 42:func:`distutils.core.setup` function use them:: 43 44 from distutils.command.build_py import build_py as _build_py 45 from distutils.core import setup 46 47 class build_py(_build_py): 48 """Specialized Python source builder.""" 49 50 # implement whatever needs to be different... 51 52 setup(cmdclass={'build_py': build_py}, 53 ...) 54 55This approach is most valuable if the new implementations must be used to use a 56particular package, as everyone interested in the package will need to have the 57new command implementation. 58 59Beginning with Python 2.4, a third option is available, intended to allow new 60commands to be added which can support existing :file:`setup.py` scripts without 61requiring modifications to the Python installation. This is expected to allow 62third-party extensions to provide support for additional packaging systems, but 63the commands can be used for anything distutils commands can be used for. A new 64configuration option, ``command_packages`` (command-line option 65:option:`!--command-packages`), can be used to specify additional packages to be 66searched for modules implementing commands. Like all distutils options, this 67can be specified on the command line or in a configuration file. This option 68can only be set in the ``[global]`` section of a configuration file, or before 69any commands on the command line. If set in a configuration file, it can be 70overridden from the command line; setting it to an empty string on the command 71line causes the default to be used. This should never be set in a configuration 72file provided with a package. 73 74This new option can be used to add any number of packages to the list of 75packages searched for command implementations; multiple package names should be 76separated by commas. When not specified, the search is only performed in the 77:mod:`distutils.command` package. When :file:`setup.py` is run with the option 78``--command-packages distcmds,buildcmds``, however, the packages 79:mod:`distutils.command`, :mod:`distcmds`, and :mod:`buildcmds` will be searched 80in that order. New commands are expected to be implemented in modules of the 81same name as the command by classes sharing the same name. Given the example 82command line option above, the command :command:`bdist_openpkg` could be 83implemented by the class :class:`distcmds.bdist_openpkg.bdist_openpkg` or 84:class:`buildcmds.bdist_openpkg.bdist_openpkg`. 85 86 87Adding new distribution types 88============================= 89 90Commands that create distributions (files in the :file:`dist/` directory) need 91to add ``(command, filename)`` pairs to ``self.distribution.dist_files`` so that 92:command:`upload` can upload it to PyPI. The *filename* in the pair contains no 93path information, only the name of the file itself. In dry-run mode, pairs 94should still be added to represent what would have been created. 95 96 97