[Python-3000] PEP: Cleaning out sys and the "interpreter" module

[Benjamin Peterson]

After a long conversation on the stdlib-sig list, I'd like to bring this
before you. For those of you not on the peps mailing list, Guido has
expressed lukewarmness (well -0.5) to the idea. However, I'd still like your
comments on my first PEP.

PEP: XXX
Title: Cleaning out sys and the "interpreter" module
Version: $Revision$
Last-Modified: $Date$
Author: Benjamin Peterson
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 4-April-2008
Python-Version: 3.0


Abstract
========

This PEP proposes a new low-level module for CPython-specific interpreter
functions in order to clean out the sys module and separate general Python
functionality from implementation details.


Rationale
=========

The sys module currently contains functions and data that can be put into
two
major groups:

1. Data and functions that are available in all Python implementations and
deal
   with the general running of a Python virtual machine.

   - argv
   - byteorder
   - path, path_hooks, meta_path, path_importer_cache, and modules
   - copyright, hexversion, version, and version_info
   - displayhook, __displayhook__
   - excepthook, __excepthook__, exc_info, and exc_clear
   - exec_prefix and prefix
   - executable
   - exit
   - flags, py3kwarning, dont_write_bytecode, and warn_options
   - getfilesystemencoding
   - get/setprofile
   - get/settrace, call_tracing
   - getwindowsversion
   - maxint and maxunicode
   - platform
   - ps1 and ps2
   - stdin, stderr, stdout, __stdin__, __stderr__, __stdout__
   - tracebacklimit


2. Data and functions that affect the CPython interpreter.

   - get/setrecursionlimit
   - get/setcheckinterval
   - _getframe and _current_frame
   - getrefcount
   - get/setdlopenflags
   - settscdumps
   - api_version
   - winver
   - dllhandle
   - float_info
   - _compact_freelists
   - _clear_type_cache
   - subversion
   - builtin_module_names
   - callstats
   - intern

The second collections of items has been steadily increasing over the years
causing clutter in sys.  Guido has even said he doesn't recognize some of
things
in it [#bug-1522]_!

Other implementations have clearly struggled with what to do about the
contents
of sys they can't implement but must to retain compatibility.  For example,
Jython's sys module has dud set/getrecursionlimit functions.  Moving these
items
items off to another module would send a clear message about what functions
need
and need not be implemented.

It has also been proposed that the contents of types module be distributed
across the standard library [#types-removal]_; the interpreter module would
provide an excellent resting place for internal types like frames and code
objects.

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

A new builtin module named "interpreter" (see `Naming`_) will be added.

The second list of items above will be split into the stdlib as follows:

The interpreter module
    - get/setrecursionlimit
    - get/setcheckinterval
    - _getframe and _current_frame
    - get/setdlopenflags
    - settscdumps
    - api_version
    - winver
    - dllhandle
    - float_info
    - _clear_type_cache
    - subversion
    - builtin_module_names
    - callstats
    - intern

The gc module:
    - getrefcount
    - _compact_freelists


Transition Plan
===============

Once implemented in 3.x, the interpreter module will be back-ported to 2.6.
Py3k warnings will be added the the sys functions it replaces.


Open Issues
===========

What should move?
-----------------

dont_write_bytecode
^^^^^^^^^^^^^^^^^^^^

Some believe that the writing of bytecode is an implementation detail and
should
be moved [#bytecode-issue]_.  The counterargument is that all current,
complete
Python implementations do write some sort of bytecode, so it is valuable to
be
able to disable it.  Also, if it is moved, some wish to put it in the imp
module.


Move to some to imp?
--------------------

It was noted that dont_write_bytecode or maybe builtin_module_names might
fit
nicely in the imp module.


Naming
------

The author proposes the name "interpreter" for the new module.  "pyvm" has
also
been suggested [#pyvm-name]_.  The name "cpython" was well liked
[#cpython-name]_.


References
==========

.. [#bug-1522]

   http://bugs.python.org/issue1522

.. [#types-removal]

   http://mail.python.org/pipermail/stdlib-sig/2008-April/000172.html

.. [#bytecode-issue]

   http://mail.python.org/pipermail/stdlib-sig/2008-April/000217.html

.. [#pyvm-name]

   http://mail.python.org/pipermail/python-3000/2007-November/011351.html

.. [#cpython-name]

   http://mail.python.org/pipermail/stdlib-sig/2008-April/000223.html

Copyright
=========

    This document has been placed in the public domain.



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-- 
Cheers,
Benjamin Peterson
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