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Python Enhancement Proposals

PEP 297 – Support for System Upgrades

Marc-André Lemburg <mal at>
Standards Track

Table of Contents

Rejection Notice

This PEP is rejected for failure to generate significant interest.


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.


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 packages without having to wait for a new patch level release of the Python interpreter to bring along the changes.

On some occasions, it may also be desirable to update modules of the standard library without going through the whole Python release cycle, e.g. in order to provide hot-fixes for security problems.

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 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.


Solution 1: Python 2.6 and up

Solution 2: all Python versions supported by distutils






Last modified: 2023-09-09 17:39:29 GMT