cpython/Tools/cases_generator
2023-04-11 15:30:05 -05:00
..
generate_cases.py gh-87092: move CFG related code from compile.c to flowgraph.c (#103021) 2023-03-31 18:17:59 +01:00
interpreter_definition.md Remove redundant words from interpreter_definition.md. (GH-103455) 2023-04-11 15:30:05 -05:00
lexer.py gh-102021 : Allow multiple input files for interpreter loop generator (#102022) 2023-03-03 20:59:21 -08:00
parser.py gh-102021 : Allow multiple input files for interpreter loop generator (#102022) 2023-03-03 20:59:21 -08:00
plexer.py GH-98831: Refactor and fix cases generator (#99526) 2022-11-17 17:06:07 -08:00
README.md gh-98831: Move DSL documentation here from ideas repo (#101629) 2023-02-06 21:03:58 -08:00
test_generator.py gh-98831: Modernize CALL_FUNCTION_EX (#101627) 2023-02-07 20:03:22 -08:00

Tooling to generate interpreters

Documentation for the instruction definitions in Python/bytecodes.c ("the DSL") is here.

What's currently here:

  • lexer.py: lexer for C, originally written by Mark Shannon
  • plexer.py: OO interface on top of lexer.py; main class: PLexer
  • parser.py: Parser for instruction definition DSL; main class Parser
  • generate_cases.py: driver script to read Python/bytecodes.c and write Python/generated_cases.c.h
  • test_generator.py: tests, require manual running using pytest

Note that there is some dummy C code at the top and bottom of Python/bytecodes.c to fool text editors like VS Code into believing this is valid C code.

A bit about the parser

The parser class uses a pretty standard recursive descent scheme, but with unlimited backtracking. The PLexer class tokenizes the entire input before parsing starts. We do not run the C preprocessor. Each parsing method returns either an AST node (a Node instance) or None, or raises SyntaxError (showing the error in the C source).

Most parsing methods are decorated with @contextual, which automatically resets the tokenizer input position when None is returned. Parsing methods may also raise SyntaxError, which is irrecoverable. When a parsing method returns None, it is possible that after backtracking a different parsing method returns a valid AST.

Neither the lexer nor the parsers are complete or fully correct. Most known issues are tersely indicated by # TODO: comments. We plan to fix issues as they become relevant.