python-peps/pep-0370.txt

PEP: 370
Title: Per user site-packages directory
Version: $Revision$
Last-Modified: $Date$
Author: Christian Heimes <christian(at)cheimes(dot)de>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 11-Jan-2008
Python-Version: 2.6, 3.0
Post-History:


Abstract
========

This PEP proposes a new a per user site-packages directory to allow
users the local installation of Python packages in their home directory.


Rationale
=========

Current Python versions don't have an unified way to install packages
into the home directory of an user (except for Mac Framework
builds). Users are either forced to ask the system administrator to
install or update a package for them or to use one of the many
workaround like Virtual Python [1]_, Working Env [2]_ or 
Virtual Env [3]_.

It's not the goal of the PEP to replace the tools or to implement
isolated installations of Python. It only implements the most common
use case of an additional site-packages directory for each user.

The feature can't be implemented using the environment variable
*PYTHONPATH*. The env var just inserts a new directory to the beginning
of *sys.path* but it doesn't parse the pth files in the directory. A
full blown site-packages path is required for several applications
and Python eggs.


Specification
=============

site directory (site-packages)

   A directory in ``sys.path``. In contrast to ordinary directories the pth
   files in the directory are processed, too.

user site directory

   A site directory inside the users' home directory. An user site
   directory is specific to a Python version. The path contains
   the version number (major and minor only).

   Mac
      ``~/Library/Python/2.6/site-packages``
   Unix
      ``~/.local/lib/python2.6/site-packages``
   Windows
      ``%APPDATA%/Python/Python26/site-packages``

user data directory

   Usually the parent directory of the user site directory. It's meant
   for Python version specific data like config files, docs, images
   and translations.

   Mac
      ``~/Library/Python/2.6``
   Unix
      ``~/.local/lib/python2.6``
   Windows
      ``%APPDATA%/Python/Python26``

user base directory

   It's located inside the user's home directory. The user site and 
   use config directory are inside the base directory. On some systems
   the directory may be shared with 3rd party apps.

   Mac
      ``~/Library/Python``
   Unix
      ``~/.local``
   Windows
      ``%APPDATA%/Python``

user script directory

   A directory for binaries and scripts. [10]_ It's shared across Python
   versions and the destination directory for scripts.

   Mac
      ``~/Library/Python/bin``
   Unix
      ``~/.local/bin``
   Windows
      ``%APPDATA%/Python/Scripts``


On Windows ``APPDATA`` was chosen because it is the most logical place for
application data. Microsoft recommands that software doesn't write to
``USERPROFILE`` [5]_ and ``My Documents`` is not suited for application data,
too. [8]_

On Linux ``~/.local`` was chosen in favor over ``~/.python`` because the
directory is already used by several other programs in analogy to
``/usr/local``. [7]_ [11]_


Implementation
==============

The site module gets a new method ``adduserpackage()`` which adds the
appropriate directory to the search path. The directory is not added if
it doesn't exist when Python is started. However the location of the 
user site directory and user base directory is stored in an internal 
variable for distutils.

The user site directory is added before the system site directories
but after Python's search paths and ``PYTHONPATH``. This setup allows
the user to install a different version of a package than the system
administrator but it prevents the user from accidently overwriting a
stdlib module. Stdlib modules can still be overwritten with
``PYTHONPATH``.

For security reasons the user site directory is *not* added to
``sys.path`` when the effective user id is not equal to the process
user id [9]_. It prevents users from injecting Python code into suid
apps.

The user site directory can be suppressed with a new option ``-s`` or
the environment variable ``PYTHONNOUSERSITE``. The feature can be
disabled globally by setting ``site.ENABLE_USER_SITE`` to the value
``False``. It must be set by editing ``site.py``. It can't be altered
``in sitecustomize.py`` or later.

``distutils.command.install`` (setup.py install) gets a new argument
``--user`` to install packages in the user site directory. The required
directories are created on demand.

``distutils.sysconfig`` will get methods to access the private variables
of site. (not yet implemented)

The Windows updater needs to be updated, too. It should create an menu
item which opens the user site directory in a new explorer windows.


Backwards Compatibility
=======================

TBD


Open Questions
==============

* Are the directories for Windows, Mac and Unix fine?

* Mac: Should framework and non-framework builds of Python use the
  same directories?

* The patch also adds a usecustomize hook to site. Is it useful and
  should it stay?

* Should the site package directory also be ignored if process gid !=
  effective gid?

* Should the Windows installer add ``%APPDATA%/Python/Scripts`` to
  ``PATH``?

* Should the base directory be configurable with an environment variable
  like ``PYTHONUSERHOME``?


Reference Implementation
========================

A reference implementation is available in the bug tracker. [4]_


Copyright
=========

This document has been placed in the public domain.


References
==========

.. [1] Virtual Python
   http://peak.telecommunity.com/DevCenter/EasyInstall#creating-a-virtual-python

.. [2]  Working Env
   http://pypi.python.org/pypi/workingenv.py
   http://blog.ianbicking.org/workingenv-revisited.html

.. [3] Virtual Env
   http://pypi.python.org/pypi/virtualenv

.. [4] reference implementation
   http://bugs.python.org/issue1799
   http://svn.python.org/view/sandbox/trunk/pep370

.. [5] MSDN: CSIDL
   http://msdn2.microsoft.com/en-us/library/bb762494.aspx

.. [6] Initial suggestion for a per user site-packages directory
   http://permalink.gmane.org/gmane.comp.python.devel/90902

.. [7] Suggestion of ~/.local/
   http://permalink.gmane.org/gmane.comp.python.devel/90925

.. [8] APPDATA discussion
   http://permalink.gmane.org/gmane.comp.python.devel/90932

.. [9] Security concerns and -s option
   http://permalink.gmane.org/gmane.comp.python.devel/91063

.. [10] Discussion about the bin directory
   http://permalink.gmane.org/gmane.comp.python.devel/91095

.. [11] freedesktop.org XGD basedir specs mentions ~/.local
   http://www.freedesktop.org/wiki/Specifications/basedir-spec

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