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<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta name="color-scheme" content="light dark"> <title>PEP 306 – How to Change Python’s Grammar | peps.python.org</title> <link rel="shortcut icon" href="../_static/py.png"> <link rel="canonical" href="https://peps.python.org/pep-0306/"> <link rel="stylesheet" href="../_static/style.css" type="text/css"> <link rel="stylesheet" href="../_static/mq.css" type="text/css"> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" media="(prefers-color-scheme: light)" id="pyg-light"> <link rel="stylesheet" href="../_static/pygments_dark.css" type="text/css" media="(prefers-color-scheme: dark)" id="pyg-dark"> <link rel="alternate" type="application/rss+xml" title="Latest PEPs" href="https://peps.python.org/peps.rss"> <meta property="og:title" content='PEP 306 – How to Change Python’s Grammar | peps.python.org'> <meta property="og:description" content="There’s more to changing Python’s grammar than editing Grammar/Grammar and Python/compile.c. 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This PEP aims to be a checklist of places that must also be fixed.</p> <p>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.</p> <p>This PEP is not intended to be an instruction manual on Python grammar hacking, for several reasons.</p> </section> <section id="rationale"> <h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2> <p>People are getting this wrong all the time; it took well over a year before someone noticed <a class="footnote-reference brackets" href="#id4" id="id2">[2]</a> that adding the floor division operator (<code class="docutils literal notranslate"><span class="pre">//</span></code>) broke the <code class="docutils literal notranslate"><span class="pre">parser</span></code> module.</p> </section> <section id="checklist"> <h2><a class="toc-backref" href="#checklist" role="doc-backlink">Checklist</a></h2> <ul class="simple"> <li><code class="docutils literal notranslate"><span class="pre">Grammar/Grammar</span></code>: OK, you’d probably worked this one out :)</li> <li><code class="docutils literal notranslate"><span class="pre">Parser/Python.asdl</span></code> may need changes to match the <code class="docutils literal notranslate"><span class="pre">Grammar</span></code>. Run <code class="docutils literal notranslate"><span class="pre">make</span></code> to regenerate <code class="docutils literal notranslate"><span class="pre">Include/Python-ast.h</span></code> and <code class="docutils literal notranslate"><span class="pre">Python/Python-ast.c</span></code>.</li> <li><code class="docutils literal notranslate"><span class="pre">Python/ast.c</span></code> will need changes to create the AST objects involved with the <code class="docutils literal notranslate"><span class="pre">Grammar</span></code> change. <code class="docutils literal notranslate"><span class="pre">Lib/compiler/ast.py</span></code> will need matching changes to the pure-python AST objects.</li> <li><code class="docutils literal notranslate"><span class="pre">Parser/pgen</span></code> needs to be rerun to regenerate <code class="docutils literal notranslate"><span class="pre">Include/graminit.h</span></code> and <code class="docutils literal notranslate"><span class="pre">Python/graminit.c</span></code>. (make should handle this for you.)</li> <li><code class="docutils literal notranslate"><span class="pre">Python/symbtable.c</span></code>: This handles the symbol collection pass that happens immediately before the compilation pass.</li> <li><code class="docutils literal notranslate"><span class="pre">Python/compile.c</span></code>: You will need to create or modify the <code class="docutils literal notranslate"><span class="pre">compiler_*</span></code> functions to generate opcodes for your productions.</li> <li>You may need to regenerate <code class="docutils literal notranslate"><span class="pre">Lib/symbol.py</span></code> and/or <code class="docutils literal notranslate"><span class="pre">Lib/token.py</span></code> and/or <code class="docutils literal notranslate"><span class="pre">Lib/keyword.py</span></code>.</li> <li>The <code class="docutils literal notranslate"><span class="pre">parser</span></code> module. Add some of your new syntax to <code class="docutils literal notranslate"><span class="pre">test_parser</span></code>, bang on <code class="docutils literal notranslate"><span class="pre">Modules/parsermodule.c</span></code> until it passes.</li> <li>Add some usage of your new syntax to <code class="docutils literal notranslate"><span class="pre">test_grammar.py</span></code>.</li> <li>The <code class="docutils literal notranslate"><span class="pre">compiler</span></code> package. A good test is to compile the standard library and test suite with the <code class="docutils literal notranslate"><span class="pre">compiler</span></code> package and then check it runs. Note that this only needs to be done in Python 2.x.</li> <li>If you’ve gone so far as to change the token structure of Python, then the <code class="docutils literal notranslate"><span class="pre">Lib/tokenizer.py</span></code> library module will need to be changed.</li> <li>Certain changes may require tweaks to the library module <code class="docutils literal notranslate"><span class="pre">pyclbr</span></code>.</li> <li>Documentation must be written!</li> <li>After everything’s been checked in, you’re likely to see a new change to <code class="docutils literal notranslate"><span class="pre">Python/Python-ast.c</span></code>. 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.</li> </ul> </section> <section id="references"> <h2><a class="toc-backref" href="#references" role="doc-backlink">References</a></h2> <aside class="footnote-list brackets"> <aside class="footnote brackets" id="id3" role="doc-footnote"> <dt class="label" id="id3">[<a href="#id1">1</a>]</dt> <dd>CPython Developer’s Guide: Changing CPython’s Grammar <a class="reference external" href="https://devguide.python.org/grammar/">https://devguide.python.org/grammar/</a></aside> <aside class="footnote brackets" id="id4" role="doc-footnote"> <dt class="label" id="id4">[<a href="#id2">2</a>]</dt> <dd>SF Bug #676521, parser module validation failure <a class="reference external" href="https://bugs.python.org/issue676521">https://bugs.python.org/issue676521</a></aside> </aside> </section> <section id="copyright"> <h2><a class="toc-backref" href="#copyright" role="doc-backlink">Copyright</a></h2> <p>This document has been placed in the public domain.</p> </section> </section> <hr class="docutils" /> <p>Source: <a class="reference external" href="https://github.com/python/peps/blob/main/peps/pep-0306.rst">https://github.com/python/peps/blob/main/peps/pep-0306.rst</a></p> <p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0306.rst">2025-02-01 08:59:27 GMT</a></p> </article> <nav id="pep-sidebar"> <h2>Contents</h2> <ul> <li><a class="reference internal" href="#note">Note</a></li> <li><a class="reference internal" href="#abstract">Abstract</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#checklist">Checklist</a></li> <li><a class="reference internal" href="#references">References</a></li> <li><a class="reference internal" href="#copyright">Copyright</a></li> </ul> <br> <a id="source" href="https://github.com/python/peps/blob/main/peps/pep-0306.rst">Page Source (GitHub)</a> </nav> </section> <script src="../_static/colour_scheme.js"></script> <script src="../_static/wrap_tables.js"></script> <script src="../_static/sticky_banner.js"></script> </body> </html>