[Python-Dev] proto-pep: How to change CPython's bytecode (original) (raw)

Brett C. bac at OCF.Berkeley.EDU
Thu Jan 6 20:50:22 CET 2005


OK, latest update with all suggest revisions (mention this is for CPython, section for known previous bytecode work).

If no one has any revisions I will submit to David for official PEP acceptance this weekend.


PEP: XXX Title: How to change CPython's bytecode Version: Revision:1.4Revision: 1.4 Revision:1.4 Last-Modified: Date:2003/09/2204:51:50Date: 2003/09/22 04:51:50 Date:2003/09/2204:51:50 Author: Brett Cannoon <brett at python.org> Status: Draft Type: Informational Content-Type: text/x-rst Created: XX-XXX-XXXX Post-History: XX-XXX-XXXX

Abstract

Python source code is compiled down to something called bytecode. This bytecode must implement enough semantics to perform the actions required by the Language Reference [#lang-ref]. As such, knowing how to add, remove, or change the bytecode is important to do properly when changing the abilities of the Python language. This PEP covers how to accomplish this in the CPython implementation of the language (referred to as simply "Python" for the rest of this PEP).

Rationale

While changing Python's bytecode is not a frequent occurence, it still happens. Having the required steps documented in a single location should make experimentation with the bytecode easier since it is not necessarily obvious what the steps are to change the bytecode.

This PEP, paired with PEP 306 [#PEP-306]_, should provide enough basic guidelines for handling any changes performed to the Python language itself in terms of syntactic changes that introduce new semantics.

Checklist

This is a rough checklist of what files need to change and how they are involved with the bytecode. All paths are given from the viewpoint of /cvsroot/python/dist/src from CVS). This list should not be considered exhaustive nor to cover all possible situations.

Suggestions for bytecode development

A few things can be done to make sure that development goes smoothly when experimenting with Python's bytecode. One is to delete all .py(c|o) files after each semantic change to Python/compile.c . That way all files will use any bytecode changes.

Make sure to run the entire testing suite [#test-suite]_. Since the regrtest.py driver recompiles all source code before a test is run it acts a good test to make sure that no existing semantics are broken.

Running parrotbench [#parrotbench]_ is also a good way to make sure existing semantics are not broken; this benchmark is practically a compliance test.

Previous experiments

Skip Montanaro presented a paper at a Python workshop on a peephole optimizer [#skip-peephole]_.

Michael Hudson has a non-active SourceForge project named Bytecodehacks [#Bytecodehacks]_ that provides functionality for playing with bytecode directly.

References

.. [#lang-ref] Python Language Reference, van Rossum & Drake (http://docs.python.org/ref/ref.html)

.. [#PEP-306] PEP 306, How to Change Python's Grammar, Hudson (http://www.python.org/peps/pep-0306.html)

.. [#dis] dis Module (http://docs.python.org/lib/module-dis.html)

.. [#test-suite] 'test' package (http://docs.python.org/lib/module-test.html)

.. [#parrotbench] Parrotbench (ftp://ftp.python.org/pub/python/parrotbench/parrotbench.tgz, http://mail.python.org/pipermail/python-dev/2003-December/041527.html)

.. [#opcode-list] Python Byte Code Instructions (http://docs.python.org/lib/bytecodes.html)

.. [#skip-peephole]

http://www.foretec.com/python/workshops/1998-11/proceedings/papers/montanaro/montanaro.html

.. [#Bytecodehacks] http://bytecodehacks.sourceforge.net/bch-docs/bch/index.html

Copyright

This document has been placed in the public domain.

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