PEP 3139 – Cleaning out sys and the “interpreter” module

PEP

3139

Title

Cleaning out sys and the “interpreter” module

Version

$Revision$

Last-Modified

$Date$

Author

Benjamin Peterson <benjamin at python.org>

Status

Rejected

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 1!

Moving these items off to another module would send a clear message to other Python implementations 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 2; 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 to 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 3. 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 4. The name “cpython” was well liked 5.