137 lines
5.0 KiB
Plaintext
137 lines
5.0 KiB
Plaintext
PEP: 250
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Title: Using site-packages on Windows
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Author: Paul Moore <p.f.moore@gmail.com>
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Status: Final
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Type: Standards Track
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Content-Type: text/x-rst
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Created: 30-Mar-2001
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Python-Version: 2.2
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Post-History: 30-Mar-2001
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Abstract
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========
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The standard Python distribution includes a directory
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``Lib/site-packages``, which is used on Unix platforms to hold
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locally installed modules and packages. The ``site.py`` module
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distributed with Python includes support for locating other
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modules in the site-packages directory.
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This PEP proposes that the site-packages directory should be used
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on the Windows platform in a similar manner.
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Motivation
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==========
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On Windows platforms, the default setting for ``sys.path`` does not
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include a directory suitable for users to install locally
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developed modules. The "expected" location appears to be the
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directory containing the Python executable itself. This is also
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the location where distutils (and distutils-generated installers)
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installs packages. Including locally developed code in the same
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directory as installed executables is not good practice.
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Clearly, users can manipulate ``sys.path``, either in a locally
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modified ``site.py``, or in a suitable ``sitecustomize.py``, or even via
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``.pth`` files. However, there should be a standard location for such
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files, rather than relying on every individual site having to set
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their own policy.
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In addition, with distutils becoming more prevalent as a means of
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distributing modules, the need for a standard install location for
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distributed modules will become more common. It would be better
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to define such a standard now, rather than later when more
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distutils-based packages exist which will need rebuilding.
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It is relevant to note that prior to Python 2.1, the site-packages
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directory was not included in ``sys.path`` for Macintosh platforms.
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This has been changed in 2.1, and Macintosh includes ``sys.path`` now,
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leaving Windows as the only major platform with no site-specific
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modules directory.
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Implementation
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==============
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The implementation of this feature is fairly trivial. All that
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would be required is a change to ``site.py``, to change the section
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setting sitedirs. The Python 2.1 version has::
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if os.sep == '/':
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sitedirs = [makepath(prefix,
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"lib",
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"python" + sys.version[:3],
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"site-packages"),
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makepath(prefix, "lib", "site-python")]
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elif os.sep == ':':
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sitedirs = [makepath(prefix, "lib", "site-packages")]
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else:
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sitedirs = [prefix]
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A suitable change would be to simply replace the last 4 lines with::
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else:
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sitedirs == [prefix, makepath(prefix, "lib", "site-packages")]
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Changes would also be required to distutils, to reflect this change
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in policy. A patch is available on Sourceforge, patch ID 445744,
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which implements this change. Note that the patch checks the Python
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version and only invokes the new behaviour for Python versions from
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2.2 onwards. This is to ensure that distutils remains compatible
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with earlier versions of Python.
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Finally, the executable code which implements the Windows installer
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used by the ``bdist_wininst`` command will need changing to use the new
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location. A separate patch is available for this, currently
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maintained by Thomas Heller.
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Notes
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=====
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- This change does not preclude packages using the current
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location -- the change only adds a directory to ``sys.path``, it
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does not remove anything.
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- Both the current location (``sys.prefix``) and the new directory
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(site-packages) are included in sitedirs, so that ``.pth`` files
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will be recognised in either location.
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- This proposal adds a single additional site-packages directory
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to sitedirs. On Unix platforms, two directories are added, one
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for version-independent files (Python code) and one for
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version-dependent code (C extensions). This is necessary on
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Unix, as the sitedirs include a common (across Python versions)
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package location, in ``/usr/local`` by default. As there is no such
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common location available on Windows, there is also no need for
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having two separate package directories.
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- If users want to keep DLLs in a single location on Windows, rather
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than keeping them in the package directory, the DLLs subdirectory
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of the Python install directory is already available for that
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purpose. Adding an extra directory solely for DLLs should not be
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necessary.
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Open Issues
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===========
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- Comments from Unix users indicate that there may be issues with
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the current setup on the Unix platform. Rather than become
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involved in cross-platform issues, this PEP specifically limits
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itself to the Windows platform, leaving changes for other platforms
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to be covered in other PEPs.
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- There could be issues with applications which embed Python. To the
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author's knowledge, there should be no problem as a result of this
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change. There have been no comments (supportive or otherwise) from
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users who embed Python.
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Copyright
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=========
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This document has been placed in the public domain.
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