[Python-Dev] PEP about sys.implementation and implementation specific user site directory

Christian Heimes lists at cheimes.de
Sat Oct 10 01:29:55 CEST 2009

Fellow Python developers!

In the light of our recent discussion about implementation specific
information and user site directory I like to start a new PEP. Much to
my regret I wasn't able to contribute to Python core development over
the past months. I hope I can find some free time over the next weeks.

Before I start with the PEP I like to reach consensus over the goal.
Alternative implementations of our beloved programming languages are
becoming more important every day. Although IronPython, Jython and PyPy
are trying hard to get as compatible to CPython as possible there are
numerous reasons for conditional code. General Python unit tests vs.
CPython specific unit tests are one reasons, implementation specific
module search paths are another. At the moment Python has no easy way to
inspect the implementation besides some code in the platform module.

I'm proposing two new attributes in the sys module: sys.implementation
and sys.userdirsuffix.


(Proposed by Nick, MAL and others.)

sys.implementation is a PyStructSequence that contains various
information about the current implementation. Some fields are required
to be present on every implementation. Implementations may choose to add
additional fields as they see fit. Some fields like compiler are useful
for introspection and are already part of sys.version. I like to include
them for the sake of completeness.

id (required):
  lower case identifier, for example "cpython", "ironpython", "jython",

name (required):
  mixed case name of the implementation, for example "CPython",
"IronPython", "Jython", "PyPy"

platform (required):
  platform or language of the implementation, for example "C", ".NET",

runtime (required):
  lower case runtime library of the implementation, for example "libc",
"msvcrt90", "java6", ".net"

compiler (required):
  verbose name of the compiler, for example "GCC 4.3.3", "Java
HotSpot(TM) Client VM (Apple Inc.)", "Mono JIT compiler version 2.0.1"



sys.userdirsuffix is an implementation and platform specific string that
is used to construct the path for the user site directory as explained
in PEP 370. The string contains the implementation name as well as the
version number of Python.

  python2.6 (CPython, Unix)
  Python26 (CPython, Windows)
  ironpython2.6 (IronPython, Unix)
  IronPython26 (IronPython, Windows)



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