blob: 06a550610d01cc161f7bfcd8cf9bef521f864bb9 [file]
<!DOCTYPE html>
<html lang="en" data-content_root="../" data-theme="auto">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
<title>PyO3 binding guidelines &#8212; Apache DataFusion in Python documentation</title>
<script data-cfasync="false">
document.documentElement.dataset.mode = localStorage.getItem("mode") || "auto";
document.documentElement.dataset.theme = localStorage.getItem("theme") || "auto";
</script>
<!--
this give us a css class that will be invisible only if js is disabled
-->
<noscript>
<style>
.pst-js-only { display: none !important; }
</style>
</noscript>
<!-- Loaded before other Sphinx assets -->
<link href="../_static/styles/theme.css?digest=8878045cc6db502f8baf" rel="stylesheet" />
<link href="../_static/styles/pydata-sphinx-theme.css?digest=8878045cc6db502f8baf" rel="stylesheet" />
<link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=8f2a1f02" />
<link rel="stylesheet" type="text/css" href="../_static/mystnb.11b39860a7a0cbfd473a3ad8a317855267ff0bd372690045ca344a6b62be495e.css" />
<link rel="stylesheet" type="text/css" href="../_static/graphviz.css?v=4ae1632d" />
<link rel="stylesheet" type="text/css" href="../_static/copybutton.css?v=76b2166b" />
<link rel="stylesheet" type="text/css" href="../_static/theme_overrides.css?v=4af573bc" />
<!-- So that users can add custom icons -->
<script src="../_static/scripts/fontawesome.js?digest=8878045cc6db502f8baf"></script>
<!-- Pre-loaded scripts that we'll load fully later -->
<link rel="preload" as="script" href="../_static/scripts/bootstrap.js?digest=8878045cc6db502f8baf" />
<link rel="preload" as="script" href="../_static/scripts/pydata-sphinx-theme.js?digest=8878045cc6db502f8baf" />
<script src="../_static/documentation_options.js?v=5929fcd5"></script>
<script src="../_static/doctools.js?v=9bcbadda"></script>
<script src="../_static/sphinx_highlight.js?v=dc90522c"></script>
<script src="../_static/clipboard.min.js?v=a7894cd8"></script>
<script src="../_static/copybutton.js?v=f281be69"></script>
<script>DOCUMENTATION_OPTIONS.pagename = 'contributor-guide/pyo3-guidelines';</script>
<script src="../_static/toc-toggle.js?v=36375f01"></script>
<link rel="icon" href="../_static/favicon.svg"/>
<link rel="index" title="Index" href="../genindex.html" />
<link rel="search" title="Search" href="../search.html" />
<link rel="next" title="FFI framing internals" href="ffi-internals.html" />
<link rel="prev" title="Introduction" href="introduction.html" />
<meta name="viewport" content="width=device-width, initial-scale=1"/>
<meta name="docsearch:language" content="en"/>
<meta name="docsearch:version" content="" />
</head>
<body data-bs-spy="scroll" data-bs-target=".bd-toc-nav" data-offset="180" data-bs-root-margin="0px 0px -60%" data-default-mode="auto">
<div id="pst-skip-link" class="skip-link d-print-none"><a href="#main-content">Skip to main content</a></div>
<div id="pst-scroll-pixel-helper"></div>
<button type="button" class="btn rounded-pill" id="pst-back-to-top">
<i class="fa-solid fa-arrow-up"></i>Back to top</button>
<dialog id="pst-search-dialog">
<form class="bd-search d-flex align-items-center"
action="../search.html"
method="get">
<i class="fa-solid fa-magnifying-glass"></i>
<input type="search"
class="form-control"
name="q"
placeholder="Search the docs ..."
aria-label="Search the docs ..."
autocomplete="off"
autocorrect="off"
autocapitalize="off"
spellcheck="false"/>
<span class="search-button__kbd-shortcut"><kbd class="kbd-shortcut__modifier">Ctrl</kbd>+<kbd>K</kbd></span>
</form>
</dialog>
<div class="pst-async-banner-revealer d-none">
<aside id="bd-header-version-warning" class="d-none d-print-none" aria-label="Version warning"></aside>
</div>
<header class="bd-header navbar navbar-expand-lg bd-navbar d-print-none">
<div class="bd-header__inner bd-page-width">
<button class="pst-navbar-icon sidebar-toggle primary-toggle" aria-label="Site navigation">
<span class="fa-solid fa-bars"></span>
</button>
<div class="col-lg-3 navbar-header-items__start">
<div class="navbar-item">
<a class="navbar-brand logo" href="../index.html">
<img src="../_static/original.svg" class="logo__image only-light" alt="Apache DataFusion in Python"/>
<img src="../_static/original_dark.svg" class="logo__image only-dark pst-js-only" alt="Apache DataFusion in Python"/>
</a></div>
</div>
<div class="col-lg-9 navbar-header-items">
<div class="me-auto navbar-header-items__center">
<div class="navbar-item">
<nav>
<ul class="bd-navbar-elements navbar-nav">
<li class="nav-item ">
<a class="nav-link nav-internal" href="../user-guide/index.html">
User Guide
</a>
</li>
<li class="nav-item ">
<a class="nav-link nav-internal" href="../extension-guide/index.html">
Extension Guide
</a>
</li>
<li class="nav-item current active">
<a class="nav-link nav-internal" href="index.html">
Contributor Guide
</a>
</li>
<li class="nav-item ">
<a class="nav-link nav-internal" href="../autoapi/index.html">
API Reference
</a>
</li>
<li class="nav-item ">
<a class="nav-link nav-internal" href="../links.html">
Links
</a>
</li>
</ul>
</nav></div>
</div>
<div class="navbar-header-items__end">
<div class="navbar-item navbar-persistent--container">
<button class="btn search-button-field search-button__button pst-js-only" title="Search" aria-label="Search" data-bs-placement="bottom" data-bs-toggle="tooltip">
<i class="fa-solid fa-magnifying-glass"></i>
<span class="search-button__default-text">Search</span>
<span class="search-button__kbd-shortcut"><kbd class="kbd-shortcut__modifier">Ctrl</kbd>+<kbd class="kbd-shortcut__modifier">K</kbd></span>
</button>
</div>
<div class="navbar-item"><ul class="navbar-icon-links"
aria-label="Icon Links">
<li class="nav-item">
<a href="https://github.com/apache/datafusion-python" title="GitHub" class="nav-link pst-navbar-icon" rel="noopener" target="_blank" data-bs-toggle="tooltip" data-bs-placement="bottom"><i class="fa-brands fa-github fa-lg" aria-hidden="true"></i>
<span class="sr-only">GitHub</span></a>
</li>
<li class="nav-item">
<a href="https://docs.rs/datafusion/latest/datafusion/" title="Rust API docs (docs.rs)" class="nav-link pst-navbar-icon" rel="noopener" target="_blank" data-bs-toggle="tooltip" data-bs-placement="bottom"><i class="fa-brands fa-rust fa-lg" aria-hidden="true"></i>
<span class="sr-only">Rust API docs (docs.rs)</span></a>
</li>
</ul></div>
<div class="navbar-item">
<button class="btn btn-sm nav-link pst-navbar-icon theme-switch-button pst-js-only" aria-label="Color mode" data-bs-title="Color mode" data-bs-placement="bottom" data-bs-toggle="tooltip">
<i class="theme-switch fa-solid fa-sun fa-lg" data-mode="light" title="Light"></i>
<i class="theme-switch fa-solid fa-moon fa-lg" data-mode="dark" title="Dark"></i>
<i class="theme-switch fa-solid fa-circle-half-stroke fa-lg" data-mode="auto" title="System Settings"></i>
</button></div>
</div>
</div>
<div class="navbar-persistent--mobile">
<button class="btn search-button-field search-button__button pst-js-only" title="Search" aria-label="Search" data-bs-placement="bottom" data-bs-toggle="tooltip">
<i class="fa-solid fa-magnifying-glass"></i>
<span class="search-button__default-text">Search</span>
<span class="search-button__kbd-shortcut"><kbd class="kbd-shortcut__modifier">Ctrl</kbd>+<kbd class="kbd-shortcut__modifier">K</kbd></span>
</button>
</div>
<button class="pst-navbar-icon sidebar-toggle secondary-toggle" aria-label="On this page">
<span class="fa-solid fa-outdent"></span>
</button>
</div>
</header>
<div class="bd-container">
<div class="bd-container__inner bd-page-width">
<dialog id="pst-primary-sidebar-modal"></dialog>
<div id="pst-primary-sidebar" class="bd-sidebar-primary bd-sidebar">
<div class="sidebar-header-items sidebar-primary__section">
<div class="sidebar-header-items__center">
<div class="navbar-item">
<nav>
<ul class="bd-navbar-elements navbar-nav">
<li class="nav-item ">
<a class="nav-link nav-internal" href="../user-guide/index.html">
User Guide
</a>
</li>
<li class="nav-item ">
<a class="nav-link nav-internal" href="../extension-guide/index.html">
Extension Guide
</a>
</li>
<li class="nav-item current active">
<a class="nav-link nav-internal" href="index.html">
Contributor Guide
</a>
</li>
<li class="nav-item ">
<a class="nav-link nav-internal" href="../autoapi/index.html">
API Reference
</a>
</li>
<li class="nav-item ">
<a class="nav-link nav-internal" href="../links.html">
Links
</a>
</li>
</ul>
</nav></div>
</div>
<div class="sidebar-header-items__end">
<div class="navbar-item"><ul class="navbar-icon-links"
aria-label="Icon Links">
<li class="nav-item">
<a href="https://github.com/apache/datafusion-python" title="GitHub" class="nav-link pst-navbar-icon" rel="noopener" target="_blank" data-bs-toggle="tooltip" data-bs-placement="bottom"><i class="fa-brands fa-github fa-lg" aria-hidden="true"></i>
<span class="sr-only">GitHub</span></a>
</li>
<li class="nav-item">
<a href="https://docs.rs/datafusion/latest/datafusion/" title="Rust API docs (docs.rs)" class="nav-link pst-navbar-icon" rel="noopener" target="_blank" data-bs-toggle="tooltip" data-bs-placement="bottom"><i class="fa-brands fa-rust fa-lg" aria-hidden="true"></i>
<span class="sr-only">Rust API docs (docs.rs)</span></a>
</li>
</ul></div>
<div class="navbar-item">
<button class="btn btn-sm nav-link pst-navbar-icon theme-switch-button pst-js-only" aria-label="Color mode" data-bs-title="Color mode" data-bs-placement="bottom" data-bs-toggle="tooltip">
<i class="theme-switch fa-solid fa-sun fa-lg" data-mode="light" title="Light"></i>
<i class="theme-switch fa-solid fa-moon fa-lg" data-mode="dark" title="Dark"></i>
<i class="theme-switch fa-solid fa-circle-half-stroke fa-lg" data-mode="auto" title="System Settings"></i>
</button></div>
</div>
</div>
<div class="sidebar-primary-items__start sidebar-primary__section">
<div class="sidebar-primary-item">
<nav class="bd-docs-nav bd-links" aria-label="Section Navigation">
<p class="bd-links__title" role="heading" aria-level="1">Section Navigation</p>
<div class="bd-toc-item navbar-nav">
<ul class="current nav bd-sidenav">
<li class="toctree-l1 has-children"><a class="reference internal" href="../user-guide/index.html">User Guide</a><details open="open"><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/introduction.html">Introduction</a></li>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/basics.html">Concepts</a></li>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/data-sources.html">Data Sources</a></li>
<li class="toctree-l2 has-children"><a class="reference internal" href="../user-guide/dataframe/index.html">DataFrames</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/dataframe/rendering.html">DataFrame Rendering</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/dataframe/execution-metrics.html">Execution Metrics</a></li>
</ul>
</details></li>
<li class="toctree-l2 has-children"><a class="reference internal" href="../user-guide/common-operations/index.html">Common Operations</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/views.html">Registering Views</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/basic-info.html">Basic Operations</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/select-and-filter.html">Column Selections</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/expressions.html">Expressions</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/joins.html">Joins</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/functions.html">Functions</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/spark-functions.html">Spark-Compatible Functions</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/aggregations.html">Aggregation</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/windows.html">Window Functions</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/common-operations/udf-and-udfa.html">User-Defined Functions</a></li>
</ul>
</details></li>
<li class="toctree-l2 has-children"><a class="reference internal" href="../user-guide/io/index.html">IO</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/io/arrow.html">Arrow</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/io/avro.html">Avro</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/io/csv.html">CSV</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/io/json.html">JSON</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/io/parquet.html">Parquet</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/io/table_provider.html">Custom Table Provider</a></li>
</ul>
</details></li>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/configuration.html">Configuration</a></li>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/extensions.html">Using extension libraries</a></li>
<li class="toctree-l2 has-children"><a class="reference internal" href="../user-guide/distributing-work/index.html">Distributing work</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/distributing-work/expressions.html">Shipping expressions to workers</a></li>
<li class="toctree-l3"><a class="reference internal" href="../user-guide/distributing-work/query-engines.html">Distributed query engines</a></li>
</ul>
</details></li>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/sql.html">SQL</a></li>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/upgrade-guides.html">Upgrade Guides</a></li>
<li class="toctree-l2"><a class="reference internal" href="../user-guide/ai-coding-assistants.html">Using AI Coding Assistants</a></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="../extension-guide/index.html">Extension Guide</a><details open="open"><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/why-ffi.html">Why FFI</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/capsule-protocol.html">The capsule protocol</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/table-providers.html">Providers and catalogs</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/functions.html">Functions and table functions</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/codecs.html">Extension codecs</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/bundles.html">Extension bundles</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/query-planners.html">Query planners</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/other-components.html">Optimizer rules and configuration</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/sessions.html">Sessions, handles, and lifetimes</a></li>
<li class="toctree-l2"><a class="reference internal" href="../extension-guide/checklist.html">Extension author checklist</a></li>
</ul>
</details></li>
<li class="toctree-l1 current active has-children"><a class="reference internal" href="index.html">Contributor Guide</a><details open="open"><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="introduction.html">Introduction</a></li>
<li class="toctree-l2 current active"><a class="current reference internal" href="#">PyO3 binding guidelines</a></li>
<li class="toctree-l2"><a class="reference internal" href="ffi-internals.html">FFI framing internals</a></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="../autoapi/index.html">API Reference</a><details open="open"><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2 has-children"><a class="reference internal" href="../autoapi/datafusion/index.html">datafusion</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/catalog/index.html">datafusion.catalog</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/context/index.html">datafusion.context</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/dataframe/index.html">datafusion.dataframe</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/dataframe_formatter/index.html">datafusion.dataframe_formatter</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/expr/index.html">datafusion.expr</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/extensions/index.html">datafusion.extensions</a></li>
<li class="toctree-l3 has-children"><a class="reference internal" href="../autoapi/datafusion/functions/index.html">datafusion.functions</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l4"><a class="reference internal" href="../autoapi/datafusion/functions/spark/index.html">datafusion.functions.spark</a></li>
</ul>
</details></li>
<li class="toctree-l3 has-children"><a class="reference internal" href="../autoapi/datafusion/input/index.html">datafusion.input</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l4"><a class="reference internal" href="../autoapi/datafusion/input/base/index.html">datafusion.input.base</a></li>
<li class="toctree-l4"><a class="reference internal" href="../autoapi/datafusion/input/location/index.html">datafusion.input.location</a></li>
</ul>
</details></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/io/index.html">datafusion.io</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/ipc/index.html">datafusion.ipc</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/object_store/index.html">datafusion.object_store</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/options/index.html">datafusion.options</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/plan/index.html">datafusion.plan</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/record_batch/index.html">datafusion.record_batch</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/substrait/index.html">datafusion.substrait</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/unparser/index.html">datafusion.unparser</a></li>
<li class="toctree-l3"><a class="reference internal" href="../autoapi/datafusion/user_defined/index.html">datafusion.user_defined</a></li>
</ul>
</details></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="../links.html">Links</a><details open="open"><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference external" href="https://github.com/apache/datafusion-python">GitHub and Issue Tracker</a></li>
<li class="toctree-l2"><a class="reference external" href="https://docs.rs/datafusion/latest/datafusion/">Rust API Docs</a></li>
<li class="toctree-l2"><a class="reference external" href="https://github.com/apache/datafusion/blob/main/CODE_OF_CONDUCT.md">Code of Conduct</a></li>
<li class="toctree-l2"><a class="reference external" href="https://github.com/apache/datafusion-python/tree/main/examples">Examples</a></li>
</ul>
</details></li>
</ul>
</div>
</nav></div>
</div>
<div class="sidebar-primary-items__end sidebar-primary__section">
<div class="sidebar-primary-item">
<div id="ethical-ad-placement"
class="flat"
data-ea-publisher="readthedocs"
data-ea-type="readthedocs-sidebar"
data-ea-manual="true">
</div></div>
</div>
</div>
<main id="main-content" class="bd-main" role="main">
<div class="bd-content">
<div class="bd-article-container">
<div class="bd-header-article d-print-none">
<div class="header-article-items header-article__inner">
<div class="header-article-items__start">
<div class="header-article-item">
<nav aria-label="Breadcrumb" class="d-print-none">
<ul class="bd-breadcrumbs">
<li class="breadcrumb-item breadcrumb-home">
<a href="../index.html" class="nav-link" aria-label="Home">
<i class="fa-solid fa-home"></i>
</a>
</li>
<li class="breadcrumb-item"><a href="index.html" class="nav-link">Contributor Guide</a></li>
<li class="breadcrumb-item active" aria-current="page"><span class="ellipsis">PyO3 binding guidelines</span></li>
</ul>
</nav>
</div>
</div>
</div>
</div>
<div id="searchbox"></div>
<article class="bd-article">
<!---
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
-->
<section id="pyo3-binding-guidelines">
<span id="pyo3-guidelines"></span><h1>PyO3 binding guidelines<a class="headerlink" href="#pyo3-binding-guidelines" title="Link to this heading">#</a></h1>
<p>Conventions for the <code class="docutils literal notranslate"><span class="pre">#[pyclass]</span></code> bindings in <code class="docutils literal notranslate"><span class="pre">crates/</span></code>. These are review
policy for this repository, not part of the extension protocol — an extension
library is free to shape its own classes differently.</p>
<section id="class-mutability">
<span id="ffi-pyclass-mutability"></span><h2>Class mutability<a class="headerlink" href="#class-mutability" title="Link to this heading">#</a></h2>
<p>PyO3 bindings should present immutable wrappers whenever a struct stores shared
or interior-mutable state. In practice this means that any <code class="docutils literal notranslate"><span class="pre">#[pyclass]</span></code>
containing an <code class="docutils literal notranslate"><span class="pre">Arc&lt;RwLock&lt;_&gt;&gt;</span></code> or similar synchronized primitive must opt into
<code class="docutils literal notranslate"><span class="pre">#[pyclass(frozen)]</span></code> unless there is a compelling reason not to.</p>
<p>The execution context illustrates the preferred pattern. <code class="docutils literal notranslate"><span class="pre">PySessionContext</span></code> in
<code class="file docutils literal notranslate"><span class="pre">src/context.rs</span></code> stays frozen even though it shares mutable state
internally via <code class="docutils literal notranslate"><span class="pre">SessionContext</span></code>. This ensures PyO3 tracks borrows correctly
while Python-facing APIs clone the inner <code class="docutils literal notranslate"><span class="pre">SessionContext</span></code> or return new
wrappers instead of mutating the existing instance in place:</p>
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="cp">#[pyclass(from_py_object, frozen, name = </span><span class="s">&quot;SessionContext&quot;</span><span class="cp">, module = </span><span class="s">&quot;datafusion&quot;</span><span class="cp">, subclass)]</span>
<span class="cp">#[derive(Clone)]</span>
<span class="k">pub</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">PySessionContext</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">pub</span><span class="w"> </span><span class="n">ctx</span><span class="p">:</span><span class="w"> </span><span class="nc">SessionContext</span><span class="p">,</span>
<span class="p">}</span>
</pre></div>
</div>
<p>Occasionally a type must remain mutable—for example when PyO3 attribute setters
need to update fields directly. In these rare cases add an inline justification
so reviewers and future contributors understand why <code class="docutils literal notranslate"><span class="pre">frozen</span></code> is unsafe to
enable. <code class="docutils literal notranslate"><span class="pre">DataTypeMap</span></code> in <code class="file docutils literal notranslate"><span class="pre">src/common/data_type.rs</span></code> includes such a
comment because PyO3 still needs to track field updates:</p>
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="c1">// TODO: This looks like this needs pyo3 tracking so leaving unfrozen for now</span>
<span class="cp">#[derive(Debug, Clone)]</span>
<span class="cp">#[pyclass(from_py_object, name = </span><span class="s">&quot;DataTypeMap&quot;</span><span class="cp">, module = </span><span class="s">&quot;datafusion.common&quot;</span><span class="cp">, subclass)]</span>
<span class="k">pub</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">DataTypeMap</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="cp">#[pyo3(get, set)]</span>
<span class="w"> </span><span class="k">pub</span><span class="w"> </span><span class="n">arrow_type</span><span class="p">:</span><span class="w"> </span><span class="nc">PyDataType</span><span class="p">,</span>
<span class="w"> </span><span class="cp">#[pyo3(get, set)]</span>
<span class="w"> </span><span class="k">pub</span><span class="w"> </span><span class="n">python_type</span><span class="p">:</span><span class="w"> </span><span class="nc">PythonType</span><span class="p">,</span>
<span class="w"> </span><span class="cp">#[pyo3(get, set)]</span>
<span class="w"> </span><span class="k">pub</span><span class="w"> </span><span class="n">sql_type</span><span class="p">:</span><span class="w"> </span><span class="nc">SqlType</span><span class="p">,</span>
<span class="p">}</span>
</pre></div>
</div>
<p>When reviewers encounter a mutable <code class="docutils literal notranslate"><span class="pre">#[pyclass]</span></code> without a comment, they should
request an explanation or ask that <code class="docutils literal notranslate"><span class="pre">frozen</span></code> be added. Keeping these wrappers
frozen by default helps avoid subtle bugs stemming from PyO3’s interior
mutability tracking.</p>
</section>
</section>
</article>
<footer class="prev-next-footer d-print-none">
<div class="prev-next-area">
<a class="left-prev"
href="introduction.html"
title="previous page">
<i class="fa-solid fa-angle-left"></i>
<div class="prev-next-info">
<p class="prev-next-subtitle">previous</p>
<p class="prev-next-title">Introduction</p>
</div>
</a>
<a class="right-next"
href="ffi-internals.html"
title="next page">
<div class="prev-next-info">
<p class="prev-next-subtitle">next</p>
<p class="prev-next-title">FFI framing internals</p>
</div>
<i class="fa-solid fa-angle-right"></i>
</a>
</div>
</footer>
</div>
<dialog id="pst-secondary-sidebar-modal"></dialog>
<div id="pst-secondary-sidebar" class="bd-sidebar-secondary bd-toc"><div class="sidebar-secondary-items sidebar-secondary__inner">
<div class="sidebar-secondary-item">
<div
id="pst-page-navigation-heading-2"
class="page-toc tocsection onthispage">
<i class="fa-solid fa-list"></i> On this page
</div>
<nav class="bd-toc-nav page-toc" aria-labelledby="pst-page-navigation-heading-2">
<ul class="visible nav section-nav flex-column">
<li class="toc-h2 nav-item toc-entry"><a class="reference internal nav-link" href="#class-mutability">Class mutability</a></li>
</ul>
</nav></div>
</div></div>
</div>
<footer class="bd-footer-content">
</footer>
</main>
</div>
</div>
<!-- Scripts loaded after <body> so the DOM is not blocked -->
<script defer src="../_static/scripts/bootstrap.js?digest=8878045cc6db502f8baf"></script>
<script defer src="../_static/scripts/pydata-sphinx-theme.js?digest=8878045cc6db502f8baf"></script>
<!-- Based on pydata_sphinx_theme/footer.html -->
<footer class="footer mt-5 mt-md-0">
<div class="container">
<div class="footer-item">
<p>Apache Arrow DataFusion, Arrow DataFusion, Apache, the Apache feather logo, and the Apache Arrow DataFusion project logo</p>
<p>are either registered trademarks or trademarks of The Apache Software Foundation in the United States and other countries.</p>
</div>
</div>
</footer>
</body>
</html>