PEP: 250
Title: Using site-packages on All Platforms
Version $Revision$
Author: gustav@morpheus.demon.co.uk (Paul Moore)
Status: Draft
Type: Standards Track
Created: 2001-03-30
Python-Version: 2.2
Post-History: 30-Mar-2001


Abstract

    The standard Python distribution includes a directory
    Lib/site-packages, which is used on Unix platforms to hold
    locally-installed modules and packages.  The site.py module
    distributed with Python includes support for locating other
    modules in the site-packages directory.

    This PEP proposes that the site-packages directory should be used
    uniformly across all platforms for locally installed modules.


Motivation

    On Windows platforms, the default setting for sys.path does not
    include a directory suitable for users to install locally
    developed modules.  The "expected" location appears to be the
    directory containing the Python executable itself.  Including
    locally developed code in the same directory as installed
    executables is not good practice.

    Clearly, users can manipulate sys.path, either in a locally
    modified site.py, or in a suitable sitecustomize.py, or even via
    .pth files.  However, there should be a standard location for such
    files, rather than relying on every individual site having to set
    their own policy.

    In addition, with distutils becoming more prevalent as a means of
    distributing modules, the need for a standard install location for
    distributed modules will become more common.  It would be better
    to define such a standard now, rather than later when more
    distutils-based packages exist which will need rebuilding.

    It is relevant to note that prior to Python 2.1, the site-packages
    directory was not included in sys.path for Macintosh platforms.
    This has been changed in 2.1, and Macintosh includes sys.path now,
    leaving Windows as the only major platform with no site-specific
    modules directory.


Implementation

    The implementation of this feature is fairly trivial.  All that
    would be required is a change to site.py, to change the section
    setting sitedirs.  The Python 2.1 version has

        if os.sep == '/':
            sitedirs = [makepath(prefix,
                                 "lib",
                                 "python" + sys.version[:3],
                                 "site-packages"),
                        makepath(prefix, "lib", "site-python")]
        elif os.sep == ':':
            sitedirs = [makepath(prefix, "lib", "site-packages")]
        else:
            sitedirs = [prefix]

    A suitable change would be to simply replace the last 4 lines with

        else:
            sitedirs == [prefix, makepath(prefix, "lib", "site-packages")]

    Changes would also be required to distutils, in the sysconfig.py
    file.  It is worth noting that this file does not seem to have
    been updated in line with the change of policy on the Macintosh,
    as of this writing.


Notes

    - This change does not preclude packages using the current
      location -- the change only adds a directory to sys.path, it
      does not remove anything.

    - Both the current location (sys.prefix) and the new directory
      (site-packages) are included in sitedirs, so that .pth files
      will be recognized in either location.

    - This proposal adds a single additional site-packages directory
      to sitedirs. On Unix platforms, two directories are added, one
      for version-independent files (Python code) and one for
      version-dependent code (C extensions). This is necessary on
      Unix, as the sitedirs include a common (across Python versions)
      package location, in /usr/local by default. As there is no such
      common location available on Windows, there is also no need for
      having two separate package directories.

    - If users want to keep DLLs in a single location on Windows,
      rather than keeping them in the package directory, the DLLs
      subdirectory of the Python install directory is available for
      that purpose. Adding an extra directory solely for DLLs should
      not be necessary.


Open Issues

    - There have been no comments on this proposal from non-Windows
      users. In the absence of such comments, it is assumed that there
      will be no adverse effects on such platforms caused by the
      proposed change. (The author knows of no reason why there should
      be).

    - There could be issues with applications which embed Python. To
      the author's knowledge, there should be no problem as a result
      of this change. Again, there have been no comments (supportive
      or otherwise) from users who embed Python.


Copyright

    This document has been placed in the public domain.



Local Variables:
mode: indented-text
indent-tabs-mode: nil
End: