1 .. _extending-distutils: 2 3 ******************* 4 Extending Distutils 5 ******************* 6 7 Distutils can be extended in various ways. Most extensions take the form of new 8 commands or replacements for existing commands. New commands may be written to 9 support new types of platform-specific packaging, for example, while 10 replacements for existing commands may be made to modify details of how the 11 command operates on a package. 12 13 Most extensions of the distutils are made within :file:`setup.py` scripts that 14 want to modify existing commands; many simply add a few file extensions that 15 should be copied into packages in addition to :file:`.py` files as a 16 convenience. 17 18 Most 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` 21 indirectly, directly subclassing the command they are replacing. Commands are 22 required 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 32 Integrating new commands 33 ======================== 34 35 There are different ways to integrate new command implementations into 36 distutils. The most difficult is to lobby for the inclusion of the new features 37 in distutils itself, and wait for (and require) a version of Python that 38 provides that support. This is really hard for many reasons. 39 40 The most common, and possibly the most reasonable for most needs, is to include 41 the 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 55 This approach is most valuable if the new implementations must be used to use a 56 particular package, as everyone interested in the package will need to have the 57 new command implementation. 58 59 Beginning with Python 2.4, a third option is available, intended to allow new 60 commands to be added which can support existing :file:`setup.py` scripts without 61 requiring modifications to the Python installation. This is expected to allow 62 third-party extensions to provide support for additional packaging systems, but 63 the commands can be used for anything distutils commands can be used for. A new 64 configuration option, ``command_packages`` (command-line option 65 :option:`!--command-packages`), can be used to specify additional packages to be 66 searched for modules implementing commands. Like all distutils options, this 67 can be specified on the command line or in a configuration file. This option 68 can only be set in the ``[global]`` section of a configuration file, or before 69 any commands on the command line. If set in a configuration file, it can be 70 overridden from the command line; setting it to an empty string on the command 71 line causes the default to be used. This should never be set in a configuration 72 file provided with a package. 73 74 This new option can be used to add any number of packages to the list of 75 packages searched for command implementations; multiple package names should be 76 separated 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 80 in that order. New commands are expected to be implemented in modules of the 81 same name as the command by classes sharing the same name. Given the example 82 command line option above, the command :command:`bdist_openpkg` could be 83 implemented by the class :class:`distcmds.bdist_openpkg.bdist_openpkg` or 84 :class:`buildcmds.bdist_openpkg.bdist_openpkg`. 85 86 87 Adding new distribution types 88 ============================= 89 90 Commands that create distributions (files in the :file:`dist/` directory) need 91 to 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 93 path information, only the name of the file itself. In dry-run mode, pairs 94 should still be added to represent what would have been created. 95 96 97
