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.. _grammar: | ||
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========================== | ||
Changing CPython's grammar | ||
========================== | ||
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Abstract | ||
======== | ||
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There's more to changing Python's grammar than editing | ||
:cpy-file:`Grammar/python.gram`. Here's a checklist. | ||
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.. note:: | ||
These instructions are for Python 3.9 and beyond. Earlier | ||
versions use a different parser technology. You probably shouldn't | ||
try to change the grammar of earlier Python versions, but if you | ||
really want to, use GitHub to track down the earlier version of this | ||
file in the devguide. | ||
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For more information on how to use the new parser, check the | ||
:ref:`section on how to use CPython's parser <parser>`. | ||
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Checklist | ||
========= | ||
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Note: sometimes things mysteriously don't work. Before giving up, try ``make clean``. | ||
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* :cpy-file:`Grammar/python.gram`: The grammar, with actions that build AST nodes. | ||
After changing it, run ``make regen-pegen`` (or ``build.bat --regen`` on Windows), | ||
to regenerate :cpy-file:`Parser/parser.c`. | ||
(This runs Python's parser generator, :cpy-file:`Tools/peg_generator`). | ||
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* :cpy-file:`Grammar/Tokens` is a place for adding new token types. After | ||
changing it, run ``make regen-token`` to regenerate | ||
:cpy-file:`Include/internal/pycore_token.h`, :cpy-file:`Parser/token.c`, | ||
:cpy-file:`Lib/token.py` and :cpy-file:`Doc/library/token-list.inc`. | ||
If you change both ``python.gram`` and ``Tokens``, | ||
run ``make regen-token`` before ``make regen-pegen``. | ||
On Windows, ``build.bat --regen`` will regenerate both at the same time. | ||
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* :cpy-file:`Parser/Python.asdl` may need changes to match the grammar. | ||
Then run ``make regen-ast`` to regenerate | ||
:cpy-file:`Include/internal/pycore_ast.h` and :cpy-file:`Python/Python-ast.c`. | ||
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* :cpy-file:`Parser/lexer/` contains the tokenization code. | ||
This is where you would add a new type of comment or string literal, for example. | ||
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* :cpy-file:`Python/ast.c` will need changes to validate AST objects | ||
involved with the grammar change. | ||
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* :cpy-file:`Python/ast_unparse.c` will need changes to unparse AST | ||
involved with the grammar change ("unparsing" is used to turn annotations | ||
into strings per :pep:`563`). | ||
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* The :ref:`compiler` has its own page. | ||
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* ``_Unparser`` in the :cpy-file:`Lib/ast.py` file may need changes | ||
to accommodate any modifications in the AST nodes. | ||
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* :cpy-file:`Doc/library/ast.rst` may need to be updated to reflect changes | ||
to AST nodes. | ||
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* Add some usage of your new syntax to ``test_grammar.py``. | ||
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* Certain changes may require tweaks to the library module :mod:`pyclbr`. | ||
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* :cpy-file:`Lib/tokenize.py` needs changes to match changes to the tokenizer. | ||
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* Documentation must be written! Specifically, one or more of the pages in | ||
:cpy-file:`Doc/reference/` will need to be updated. | ||
This document is now part of the | ||
`CPython Internals Docs <https://github.com/python/cpython/blob/main/InternalDocs/changing_grammar.md>`_. |