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| PEP: 306 | |
| Title: How to Change Python's Grammar | |
| Version: $Revision$ | |
| Last-Modified: $Date$ | |
| Author: Michael Hudson <mwh@python.net>, Jack Diederich <jackdied@gmail.com>, Nick Coghlan <ncoghlan@gmail.com>, Benjamin Peterson <benjamin@python.org> | |
| Status: Withdrawn | |
| Type: Informational | |
| Content-Type: text/x-rst | |
| Created: 29-Jan-2003 | |
| Post-History: 30-Jan-2003 | |
| Note | |
| ==== | |
| This PEP has been moved to the Python dev guide [1]_. | |
| 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 | |
| grammar hacking, for several reasons. | |
| Rationale | |
| ========= | |
| People are getting this wrong all the time; it took well over a | |
| year before someone noticed [2]_ that adding the floor division | |
| operator (``//``) broke the ``parser`` module. | |
| Checklist | |
| ========= | |
| - ``Grammar/Grammar``: OK, you'd probably worked this one out :) | |
| - ``Parser/Python.asdl`` may need changes to match the ``Grammar``. Run | |
| ``make`` to regenerate ``Include/Python-ast.h`` and | |
| ``Python/Python-ast.c``. | |
| - ``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`` | |
| and ``Python/graminit.c``. (make should handle this for you.) | |
| - ``Python/symbtable.c``: This handles the symbol collection pass | |
| that happens immediately before the compilation pass. | |
| - ``Python/compile.c``: You will need to create or modify the | |
| ``compiler_*`` functions to generate opcodes for your productions. | |
| - You may need to regenerate ``Lib/symbol.py`` and/or ``Lib/token.py`` | |
| and/or ``Lib/keyword.py``. | |
| - The ``parser`` module. Add some of your new syntax to ``test_parser``, | |
| bang on ``Modules/parsermodule.c`` until it passes. | |
| - Add some usage of your new syntax to ``test_grammar.py``. | |
| - The ``compiler`` package. A good test is to compile the standard | |
| library and test suite with the ``compiler`` package and then check | |
| it runs. Note that this only needs to be done in Python 2.x. | |
| - 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. | |
| - Certain changes may require tweaks to the library module | |
| ``pyclbr``. | |
| - 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. | |
| References | |
| ========== | |
| .. [1] CPython Developer's Guide: Changing CPython's Grammar | |
| https://devguide.python.org/grammar/ | |
| .. [2] SF Bug #676521, parser module validation failure | |
| https://bugs.python.org/issue676521 | |
| Copyright | |
| ========= | |
| This document has been placed in the public domain. | |
| .. | |
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