[Python-checkins] CVS: python/nondist/peps pep-0250.txt,NONE,1.1

[Barry Warsaw]

Update of /cvsroot/python/python/nondist/peps
In directory usw-pr-cvs1:/tmp/cvs-serv1982

Added Files:
	pep-0250.txt 
Log Message:
PEP 250, Using site-packages on All Platforms, Paul Moore


--- NEW FILE: pep-0250.txt ---
PEP: 250
Title: Using site-packages on All Platforms
Version $Revision: 1.1 $
Author: gustav@morpheus.demon.co.uk (Paul Moore)
Status: Draft
Type: Standards Track
Created: 2001-03-30
Python-Version: 2.2
Post-History:


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 == [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

    1. It would be better if this change could be included in Python
       2.1, as changing something of this nature is better done
       sooner, rather than later, to reduce the backward-compatibility
       burden. This is extremely unlikely to happen at this late stage
       in the release cycle, however.

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

    3. In the Windows distribution of Python 2.1 (beta 1), the
       Lib\site-packages directory has been removed.  It would need to
       be reinstated.


Copyright

    This document has been placed in the public domain.



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