python-peps/pep-0297.txt

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PEP: 297
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Title: Support for System Upgrades
Version: $Revision$
Last-Modified: $Date$
Author: mal@lemburg.com (Marc-André Lemburg)
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Status: Draft
Type: Standards Track
Python-Version: 2.3
Created: 19-Jul-2001
Post-History:
Abstract
This PEP proposes strategies to allow the Python standard library
to be upgraded in parts without having to reinstall the complete
distribution or having to wait for a new patch level release.
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Problem
Python currently does not allow overriding modules or packages in
the standard library per default. Even though this is possible by
defining a PYTHONPATH environment variable (the paths defined in
this variable are prepended to the Python standard library path),
there is no standard way of achieving this without changing the
configuration.
Since Python's standard library is starting to host packages which
are also available separately, e.g. the distutils, email and PyXML
packages, which can also be installed independently of the Python
distribution, it is desirable to have an option to upgrade these
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packages without having to wait for a new patch level release of
the Python interpreter to bring along the changes.
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Proposed Solutions
This PEP proposes two different but not necessarily conflicting
solutions:
1. Adding a new standard search path to sys.path:
$stdlibpath/system-packages just before the $stdlibpath
entry. This complements the already existing entry for site
add-ons $stdlibpath/site-packages which is appended to the
sys.path at interpreter startup time.
To make use of this new standard location, distutils will need
to grow support for installing certain packages in
$stdlibpath/system-packages rather than the standard location
for third-party packages $stdlibpath/site-packages.
2. Tweaking distutils to install directly into $stdlibpath for the
system upgrades rather than into $stdlibpath/site-packages.
The first solution has a few advantages over the second:
* upgrades can be easily identified (just look in
$stdlibpath/system-packages)
* upgrades can be de-installed without affecting the rest
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of the interpreter installation
* modules can be virtually removed from packages; this is
due to the way Python imports packages: once it finds the
top-level package directory it stay in this directory for
all subsequent package submodule imports
* the approach has an overall much cleaner design than the
hackish install on top of an existing installation approach
The only advantages of the second approach are that the Python
interpreter does not have to changed and that it works with
older Python versions.
Both solutions require changes to distutils. These changes can
also be implemented by package authors, but it would be better to
define a standard way of switching on the proposed behaviour.
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Scope
Solution 1: Python 2.3 and up
Solution 2: all Python versions supported by distutils
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Credits
None
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References
None
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Copyright
This document has been placed in the public domain.
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