245 lines
17 KiB
HTML
245 lines
17 KiB
HTML
|
|
|||
|
|
<!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 336 – Make None Callable | peps.python.org</title>
|
|||
|
|
<link rel="shortcut icon" href="../_static/py.png">
|
|||
|
|
<link rel="canonical" href="https://peps.python.org/pep-0336/">
|
|||
|
|
<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 336 – Make None Callable | peps.python.org'>
|
|||
|
|
<meta property="og:description" content="None should be a callable object that when called with any arguments has no side effect and returns None.">
|
|||
|
|
<meta property="og:type" content="website">
|
|||
|
|
<meta property="og:url" content="https://peps.python.org/pep-0336/">
|
|||
|
|
<meta property="og:site_name" content="Python Enhancement Proposals (PEPs)">
|
|||
|
|
<meta property="og:image" content="https://peps.python.org/_static/og-image.png">
|
|||
|
|
<meta property="og:image:alt" content="Python PEPs">
|
|||
|
|
<meta property="og:image:width" content="200">
|
|||
|
|
<meta property="og:image:height" content="200">
|
|||
|
|
<meta name="description" content="None should be a callable object that when called with any arguments has no side effect and returns None.">
|
|||
|
|
<meta name="theme-color" content="#3776ab">
|
|||
|
|
</head>
|
|||
|
|
<body>
|
|||
|
|
|
|||
|
|
<svg xmlns="http://www.w3.org/2000/svg" style="display: none;">
|
|||
|
|
<symbol id="svg-sun-half" viewBox="0 0 24 24" pointer-events="all">
|
|||
|
|
<title>Following system colour scheme</title>
|
|||
|
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none"
|
|||
|
|
stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
|
|||
|
|
<circle cx="12" cy="12" r="9"></circle>
|
|||
|
|
<path d="M12 3v18m0-12l4.65-4.65M12 14.3l7.37-7.37M12 19.6l8.85-8.85"></path>
|
|||
|
|
</svg>
|
|||
|
|
</symbol>
|
|||
|
|
<symbol id="svg-moon" viewBox="0 0 24 24" pointer-events="all">
|
|||
|
|
<title>Selected dark colour scheme</title>
|
|||
|
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none"
|
|||
|
|
stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
|
|||
|
|
<path stroke="none" d="M0 0h24v24H0z" fill="none"></path>
|
|||
|
|
<path d="M12 3c.132 0 .263 0 .393 0a7.5 7.5 0 0 0 7.92 12.446a9 9 0 1 1 -8.313 -12.454z"></path>
|
|||
|
|
</svg>
|
|||
|
|
</symbol>
|
|||
|
|
<symbol id="svg-sun" viewBox="0 0 24 24" pointer-events="all">
|
|||
|
|
<title>Selected light colour scheme</title>
|
|||
|
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none"
|
|||
|
|
stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
|
|||
|
|
<circle cx="12" cy="12" r="5"></circle>
|
|||
|
|
<line x1="12" y1="1" x2="12" y2="3"></line>
|
|||
|
|
<line x1="12" y1="21" x2="12" y2="23"></line>
|
|||
|
|
<line x1="4.22" y1="4.22" x2="5.64" y2="5.64"></line>
|
|||
|
|
<line x1="18.36" y1="18.36" x2="19.78" y2="19.78"></line>
|
|||
|
|
<line x1="1" y1="12" x2="3" y2="12"></line>
|
|||
|
|
<line x1="21" y1="12" x2="23" y2="12"></line>
|
|||
|
|
<line x1="4.22" y1="19.78" x2="5.64" y2="18.36"></line>
|
|||
|
|
<line x1="18.36" y1="5.64" x2="19.78" y2="4.22"></line>
|
|||
|
|
</svg>
|
|||
|
|
</symbol>
|
|||
|
|
</svg>
|
|||
|
|
<script>
|
|||
|
|
|
|||
|
|
document.documentElement.dataset.colour_scheme = localStorage.getItem("colour_scheme") || "auto"
|
|||
|
|
</script>
|
|||
|
|
<section id="pep-page-section">
|
|||
|
|
<header>
|
|||
|
|
<h1>Python Enhancement Proposals</h1>
|
|||
|
|
<ul class="breadcrumbs">
|
|||
|
|
<li><a href="https://www.python.org/" title="The Python Programming Language">Python</a> » </li>
|
|||
|
|
<li><a href="../pep-0000/">PEP Index</a> » </li>
|
|||
|
|
<li>PEP 336</li>
|
|||
|
|
</ul>
|
|||
|
|
<button id="colour-scheme-cycler" onClick="setColourScheme(nextColourScheme())">
|
|||
|
|
<svg aria-hidden="true" class="colour-scheme-icon-when-auto"><use href="#svg-sun-half"></use></svg>
|
|||
|
|
<svg aria-hidden="true" class="colour-scheme-icon-when-dark"><use href="#svg-moon"></use></svg>
|
|||
|
|
<svg aria-hidden="true" class="colour-scheme-icon-when-light"><use href="#svg-sun"></use></svg>
|
|||
|
|
<span class="visually-hidden">Toggle light / dark / auto colour theme</span>
|
|||
|
|
</button>
|
|||
|
|
</header>
|
|||
|
|
<article>
|
|||
|
|
<section id="pep-content">
|
|||
|
|
<h1 class="page-title">PEP 336 – Make None Callable</h1>
|
|||
|
|
<dl class="rfc2822 field-list simple">
|
|||
|
|
<dt class="field-odd">Author<span class="colon">:</span></dt>
|
|||
|
|
<dd class="field-odd">Andrew McClelland <eternalsquire at comcast.net></dd>
|
|||
|
|
<dt class="field-even">Status<span class="colon">:</span></dt>
|
|||
|
|
<dd class="field-even"><abbr title="Formally declined and will not be accepted">Rejected</abbr></dd>
|
|||
|
|
<dt class="field-odd">Type<span class="colon">:</span></dt>
|
|||
|
|
<dd class="field-odd"><abbr title="Normative PEP with a new feature for Python, implementation change for CPython or interoperability standard for the ecosystem">Standards Track</abbr></dd>
|
|||
|
|
<dt class="field-even">Created<span class="colon">:</span></dt>
|
|||
|
|
<dd class="field-even">28-Oct-2004</dd>
|
|||
|
|
<dt class="field-odd">Post-History<span class="colon">:</span></dt>
|
|||
|
|
<dd class="field-odd"><p></p></dd>
|
|||
|
|
</dl>
|
|||
|
|
<hr class="docutils" />
|
|||
|
|
<section id="contents">
|
|||
|
|
<details><summary>Table of Contents</summary><ul class="simple">
|
|||
|
|
<li><a class="reference internal" href="#abstract">Abstract</a></li>
|
|||
|
|
<li><a class="reference internal" href="#bdfl-pronouncement">BDFL Pronouncement</a></li>
|
|||
|
|
<li><a class="reference internal" href="#motivation">Motivation</a></li>
|
|||
|
|
<li><a class="reference internal" href="#rationale">Rationale</a></li>
|
|||
|
|
<li><a class="reference internal" href="#how-to-use">How To Use</a></li>
|
|||
|
|
<li><a class="reference internal" href="#references">References</a></li>
|
|||
|
|
<li><a class="reference internal" href="#copyright">Copyright</a></li>
|
|||
|
|
</ul>
|
|||
|
|
</details></section>
|
|||
|
|
<section id="abstract">
|
|||
|
|
<h2><a class="toc-backref" href="#abstract" role="doc-backlink">Abstract</a></h2>
|
|||
|
|
<p><code class="docutils literal notranslate"><span class="pre">None</span></code> should be a callable object that when called with any
|
|||
|
|
arguments has no side effect and returns <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="bdfl-pronouncement">
|
|||
|
|
<h2><a class="toc-backref" href="#bdfl-pronouncement" role="doc-backlink">BDFL Pronouncement</a></h2>
|
|||
|
|
<p>This PEP is rejected. It is considered a feature that <code class="docutils literal notranslate"><span class="pre">None</span></code> raises
|
|||
|
|
an error when called. The proposal falls short in tests for
|
|||
|
|
obviousness, clarity, explicitness, and necessity. The provided Switch
|
|||
|
|
example is nice but easily handled by a simple lambda definition.
|
|||
|
|
See python-dev discussion on 17 June 2005 <a class="footnote-reference brackets" href="#id2" id="id1">[1]</a>.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="motivation">
|
|||
|
|
<h2><a class="toc-backref" href="#motivation" role="doc-backlink">Motivation</a></h2>
|
|||
|
|
<p>To allow a programming style for selectable actions that is more
|
|||
|
|
in accordance with the minimalistic functional programming goals
|
|||
|
|
of the Python language.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="rationale">
|
|||
|
|
<h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2>
|
|||
|
|
<p>Allow the use of <code class="docutils literal notranslate"><span class="pre">None</span></code> in method tables as a universal no effect
|
|||
|
|
rather than either (1) checking a method table entry against <code class="docutils literal notranslate"><span class="pre">None</span></code>
|
|||
|
|
before calling, or (2) writing a local no effect method with
|
|||
|
|
arguments similar to other functions in the table.</p>
|
|||
|
|
<p>The semantics would be effectively:</p>
|
|||
|
|
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">None</span><span class="p">:</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">):</span>
|
|||
|
|
<span class="k">pass</span>
|
|||
|
|
</pre></div>
|
|||
|
|
</div>
|
|||
|
|
</section>
|
|||
|
|
<section id="how-to-use">
|
|||
|
|
<h2><a class="toc-backref" href="#how-to-use" role="doc-backlink">How To Use</a></h2>
|
|||
|
|
<p>Before, checking function table entry against <code class="docutils literal notranslate"><span class="pre">None</span></code>:</p>
|
|||
|
|
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Select</span><span class="p">:</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">a</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'a'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">b</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'b'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">c</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'c'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="n">function</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">1</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span><span class="p">,</span>
|
|||
|
|
<span class="mi">2</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span><span class="p">,</span>
|
|||
|
|
<span class="mi">3</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">c</span>
|
|||
|
|
<span class="p">}</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="nb">input</span><span class="p">,</span> <span class="kc">None</span><span class="p">)</span>
|
|||
|
|
<span class="k">if</span> <span class="n">function</span><span class="p">:</span> <span class="k">return</span> <span class="n">function</span><span class="p">(</span><span class="nb">input</span><span class="p">)</span>
|
|||
|
|
</pre></div>
|
|||
|
|
</div>
|
|||
|
|
<p>Before, using a local no effect method:</p>
|
|||
|
|
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Select</span><span class="p">:</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">a</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'a'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">b</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'b'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">c</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'c'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">nop</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="k">pass</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="k">return</span> <span class="p">{</span> <span class="mi">1</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span><span class="p">,</span>
|
|||
|
|
<span class="mi">2</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span><span class="p">,</span>
|
|||
|
|
<span class="mi">3</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">c</span>
|
|||
|
|
<span class="p">}</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="nb">input</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">nop</span><span class="p">)(</span><span class="nb">input</span><span class="p">)</span>
|
|||
|
|
</pre></div>
|
|||
|
|
</div>
|
|||
|
|
<p>After:</p>
|
|||
|
|
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Select</span><span class="p">:</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">a</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'a'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">b</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'b'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="nf">c</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="nb">print</span> <span class="s1">'c'</span>
|
|||
|
|
|
|||
|
|
<span class="k">def</span> <span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">):</span>
|
|||
|
|
<span class="k">return</span> <span class="p">{</span> <span class="mi">1</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span><span class="p">,</span>
|
|||
|
|
<span class="mi">2</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span><span class="p">,</span>
|
|||
|
|
<span class="mi">3</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">c</span>
|
|||
|
|
<span class="p">}</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="nb">input</span><span class="p">,</span> <span class="kc">None</span><span class="p">)(</span><span class="nb">input</span><span class="p">)</span>
|
|||
|
|
</pre></div>
|
|||
|
|
</div>
|
|||
|
|
</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="id2" role="doc-footnote">
|
|||
|
|
<dt class="label" id="id2">[<a href="#id1">1</a>]</dt>
|
|||
|
|
<dd>Raymond Hettinger, Propose to reject PEP 336 – Make None Callable
|
|||
|
|
<a class="reference external" href="https://mail.python.org/pipermail/python-dev/2005-June/054280.html">https://mail.python.org/pipermail/python-dev/2005-June/054280.html</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-0336.rst">https://github.com/python/peps/blob/main/peps/pep-0336.rst</a></p>
|
|||
|
|
<p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0336.rst">2023-09-09 17:39:29 GMT</a></p>
|
|||
|
|
|
|||
|
|
</article>
|
|||
|
|
<nav id="pep-sidebar">
|
|||
|
|
<h2>Contents</h2>
|
|||
|
|
<ul>
|
|||
|
|
<li><a class="reference internal" href="#abstract">Abstract</a></li>
|
|||
|
|
<li><a class="reference internal" href="#bdfl-pronouncement">BDFL Pronouncement</a></li>
|
|||
|
|
<li><a class="reference internal" href="#motivation">Motivation</a></li>
|
|||
|
|
<li><a class="reference internal" href="#rationale">Rationale</a></li>
|
|||
|
|
<li><a class="reference internal" href="#how-to-use">How To Use</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-0336.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>
|