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64 lines
2.7 KiB
Markdown
64 lines
2.7 KiB
Markdown
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# Changing CPython's grammar
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There's more to changing Python's grammar than editing
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[`Grammar/python.gram`](../Grammar/python.gram).
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Below is a checklist of things that may need to change.
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> [!NOTE]
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>
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> Many of these changes require re-generating some of the derived
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> files. If things mysteriously don't work, it may help to run
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> ``make clean``.
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## Checklist
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* [`Grammar/python.gram`](../Grammar/python.gram): The grammar definition,
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with actions that build AST nodes.
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After changing it, run ``make regen-pegen`` (or ``build.bat --regen`` on Windows),
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to regenerate [`Parser/parser.c`](../Parser/parser.c).
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(This runs Python's parser generator, [`Tools/peg_generator`](../Tools/peg_generator)).
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* [`Grammar/Tokens`](../Grammar/Tokens) is a place for adding new token types. After
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changing it, run ``make regen-token`` to regenerate
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[`Include/internal/pycore_token.h`](../Include/internal/pycore_token.h),
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[`Parser/token.c`](../Parser/token.c), [`Lib/token.py`](../Lib/token.py)
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and [`Doc/library/token-list.inc`](../Doc/library/token-list.inc).
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If you change both ``python.gram`` and ``Tokens``, run ``make regen-token``
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before ``make regen-pegen``.
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On Windows, ``build.bat --regen`` will regenerate both at the same time.
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* [`Parser/Python.asdl`](../Parser/Python.asdl) may need changes to match the grammar.
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Then run ``make regen-ast`` to regenerate
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[`Include/internal/pycore_ast.h`](../Include/internal/pycore_ast.h) and
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[`Python/Python-ast.c`](../Python/Python-ast.c).
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* [`Parser/lexer/`](../Parser/lexer/) contains the tokenization code.
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This is where you would add a new type of comment or string literal, for example.
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* [`Python/ast.c`](../Python/ast.c) will need changes to validate AST objects
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involved with the grammar change.
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* [`Python/ast_unparse.c`](../Python/ast_unparse.c) will need changes to unparse
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AST involved with the grammar change ("unparsing" is used to turn annotations
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into strings per [PEP 563](https://peps.python.org/pep-0563/).
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* The [`compiler`](compiler.md) may need to change when there are changes
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to the `AST`.
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* ``_Unparser`` in the [`Lib/ast.py`](../Lib/ast.py) file may need changes
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to accommodate any modifications in the AST nodes.
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* [`Doc/library/ast.rst`](../Doc/library/ast.rst) may need to be updated
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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
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[`pyclbr`](https://docs.python.org/3/library/pyclbr.html#module-pyclbr).
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* [`Lib/tokenize.py`](../Lib/tokenize.py) needs changes to match changes
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to the tokenizer.
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* Documentation must be written! Specifically, one or more of the pages in
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[`Doc/reference/`](../Doc/reference/) will need to be updated.
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