[Python-Dev] PEP: per user site-packages directory (original) (raw)
Christian Heimes lists at cheimes.de
Sat Jan 12 00:27:43 CET 2008
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MA Lemburg has suggested a per user site-packages directory in the "pkgutil, pkg_resource and Python 3.0 name space packages" thread. I've written a short PEP about it for Python 2.6 and 3.0.
PEP: XXX Title: Per user site-packages directory Version: RevisionRevisionRevision Last-Modified: DateDateDate 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).
Windows: %APPDATA%/Python/Python26/site-packages Mac: ~/Library/Python/2.6/site-packages Unix: ~/.local/lib/python2.6/site-packages
user configuration directory
Usually the parent directory of the user site directory. It's meant for Python version specific data like config files.
Windows: %APPDATA%/Python/Python26 Mac: ~/Library/Python/2.6 Unix: ~/.local/lib/python2.6
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.
Windows: %APPDATA%/Python Mac: ~/Library/Python Unix: ~/.local
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]_
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.
distutils.command.install (setup.py install) gets a new argument --user to install packages in the user site directory. The required directories are created by install.
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?
Reference Implementation
A reference implementation is available in the bug tracker. [4]_
Acknowledgments
The implementation of this PEP, if accepted, is sponsored by Google through the Google Summer of Code program.
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
.. [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
.. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 coding: utf-8 End:
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