python-peps/pep-0306.txt

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PEP: 306
Title: How to Change Python's Grammar
Version: $Revision$
Last-Modified: $Date$
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Author: Michael Hudson <mwh@python.net>, Jack Diederich <jackdied@gmail.com>, Nick Coghlan <ncoghlan@gmail.com>, Benjamin Peterson <benjamin@python.org>
Status: Withdrawn
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Type: Informational
Content-Type: text/plain
Created: 29-Jan-2003
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Post-History: 30-Jan-2003
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Note
This PEP has been moved to the Python dev guide.
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Abstract
There's more to changing Python's grammar than editing
Grammar/Grammar and Python/compile.c. This PEP aims to be a
checklist of places that must also be fixed.
It is probably incomplete. If you see omissions, just add them if
you can -- you are not going to offend the author's sense of
ownership. Otherwise submit a bug or patch and assign it to mwh.
This PEP is not intended to be an instruction manual on Python
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grammar hacking, for several reasons.
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Rationale
People are getting this wrong all the time; it took well over a
year before someone noticed[1] that adding the floor division
operator (//) broke the parser module.
Checklist
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__ Grammar/Grammar: OK, you'd probably worked this one out :)
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__ Parser/Python.asdl may need changes to match the Grammar. Run
make to regenerate Include/Python-ast.h and
Python/Python-ast.c.
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__ Python/ast.c will need changes to create the AST objects
involved with the Grammar change. Lib/compiler/ast.py will
need matching changes to the pure-python AST objects.
__ Parser/pgen needs to be rerun to regenerate Include/graminit.h
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and Python/graminit.c. (make should handle this for you.)
__ Python/symbtable.c: This handles the symbol collection pass
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that happens immediately before the compilation pass.
__ Python/compile.c: You will need to create or modify the
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compiler_* functions to generate opcodes for your productions.
__ You may need to regenerate Lib/symbol.py and/or Lib/token.py
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and/or Lib/keyword.py.
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__ The parser module. Add some of your new syntax to test_parser,
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bang on Modules/parsermodule.c until it passes.
__ Add some usage of your new syntax to test_grammar.py
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__ The compiler package. A good test is to compile the standard
library and test suite with the compiler package and then check
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it runs. Note that this only needs to be done in Python 2.x.
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__ If you've gone so far as to change the token structure of
Python, then the Lib/tokenizer.py library module will need to
be changed.
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__ Certain changes may require tweaks to the library module
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pyclbr.
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__ Documentation must be written!
__ After everything's been checked in, you're likely to see a new
change to Python/Python-ast.c. This is because this
(generated) file contains the SVN version of the source from
which it was generated. There's no way to avoid this; you just
have to submit this file separately.
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References
[1] SF Bug #676521, parser module validation failure
http://www.python.org/sf/676521
Copyright
This document has been placed in the public domain.
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