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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 559 – Built-in noop() | peps.python.org</title> <link rel="shortcut icon" href="../_static/py.png"> <link rel="canonical" href="https://peps.python.org/pep-0559/"> <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 559 – Built-in noop() | peps.python.org'> <meta property="og:description" content="This PEP proposes adding a 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<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 559 – Built-in noop()</h1> <dl class="rfc2822 field-list simple"> <dt class="field-odd">Author<span class="colon">:</span></dt> <dd class="field-odd">Barry Warsaw <barry at python.org></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">08-Sep-2017</dd> <dt class="field-odd">Python-Version<span class="colon">:</span></dt> <dd class="field-odd">3.7</dd> <dt class="field-even">Post-History<span class="colon">:</span></dt> <dd class="field-even">09-Sep-2017</dd> <dt class="field-odd">Resolution<span class="colon">:</span></dt> <dd class="field-odd"><a class="reference external" href="https://mail.python.org/pipermail/python-dev/2017-September/149438.html">Python-Dev message</a></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="#rationale">Rationale</a></li> <li><a class="reference internal" href="#implementation">Implementation</a></li> <li><a class="reference internal" href="#rejected-alternatives">Rejected alternatives</a><ul> <li><a class="reference internal" href="#noop-returns-something"><code class="docutils literal notranslate"><span class="pre">noop()</span></code> returns something</a></li> </ul> </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>This PEP proposes adding a new built-in function called <code class="docutils literal notranslate"><span class="pre">noop()</span></code> which does nothing but return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p> </section> <section id="rationale"> <h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2> <p>It is trivial to implement a no-op function in Python. It’s so easy in fact that many people do it many times over and over again. It would be useful in many cases to have a common built-in function that does nothing.</p> <p>One use case would be for <a class="pep reference internal" href="../pep-0553/" title="PEP 553 – Built-in breakpoint()">PEP 553</a>, where you could set the breakpoint environment variable to the following in order to effectively disable it:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ setenv PYTHONBREAKPOINT=noop </pre></div> </div> </section> <section id="implementation"> <h2><a class="toc-backref" href="#implementation" role="doc-backlink">Implementation</a></h2> <p>The Python equivalent of the <code class="docutils literal notranslate"><span class="pre">noop()</span></code> function is exactly:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">noop</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kws</span><span class="p">):</span> <span class="k">return</span> <span class="kc">None</span> </pre></div> </div> <p>The C built-in implementation is available as a pull request <a class="footnote-reference brackets" href="#id2" id="id1">[1]</a>.</p> </section> <section id="rejected-alternatives"> <h2><a class="toc-backref" href="#rejected-alternatives" role="doc-backlink">Rejected alternatives</a></h2> <section id="noop-returns-something"> <h3><a class="toc-backref" href="#noop-returns-something" role="doc-backlink"><code class="docutils literal notranslate"><span class="pre">noop()</span></code> returns something</a></h3> <p>YAGNI.</p> <p>This is rejected because it complicates the semantics. For example, if you always return both <code class="docutils literal notranslate"><span class="pre">*args</span></code> and <code class="docutils literal notranslate"><span class="pre">**kws</span></code>, what do you return when none of those are given? Returning a tuple of <code class="docutils literal notranslate"><span class="pre">((),</span> <span class="pre">{})</span></code> is kind of ugly, but provides consistency. But you might also want to just return <code class="docutils literal notranslate"><span class="pre">None</span></code> since that’s also conceptually what the function was passed.</p> <p>Or, what if you pass in exactly one positional argument, e.g. <code class="docutils literal notranslate"><span class="pre">noop(7)</span></code>. Do you return <code class="docutils literal notranslate"><span class="pre">7</span></code> or <code class="docutils literal notranslate"><span class="pre">((7,),</span> <span class="pre">{})</span></code>? And so on.</p> <p>The author claims that you won’t ever need the return value of <code class="docutils literal notranslate"><span class="pre">noop()</span></code> so it will always return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p> <p>Coghlan’s Dialogs (edited for formatting):</p> <blockquote> <div>My counterargument to this would be <code class="docutils literal notranslate"><span class="pre">map(noop,</span> <span class="pre">iterable)</span></code>, <code class="docutils literal notranslate"><span class="pre">sorted(iterable,</span> <span class="pre">key=noop)</span></code>, etc. (<code class="docutils literal notranslate"><span class="pre">filter</span></code>, <code class="docutils literal notranslate"><span class="pre">max</span></code>, and <code class="docutils literal notranslate"><span class="pre">min</span></code> all accept callables that accept a single argument, as do many of the itertools operations).<p>Making <code class="docutils literal notranslate"><span class="pre">noop()</span></code> a useful default function in those cases just needs the definition to be:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">noop</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">):</span> <span class="k">return</span> <span class="n">args</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="k">if</span> <span class="n">args</span> <span class="k">else</span> <span class="kc">None</span> </pre></div> </div> <p>The counterargument to the counterargument is that using <code class="docutils literal notranslate"><span class="pre">None</span></code> as the default in all these cases is going to be faster, since it lets the algorithm skip the callback entirely, rather than calling it and having it do nothing useful.</p> </div></blockquote> </section> </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><a class="reference external" href="https://github.com/python/cpython/pull/3480">https://github.com/python/cpython/pull/3480</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-0559.rst">https://github.com/python/peps/blob/main/peps/pep-0559.rst</a></p> <p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0559.rst">2025-02-01 08:55:40 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="#rationale">Rationale</a></li> <li><a class="reference internal" href="#implementation">Implementation</a></li> <li><a class="reference internal" href="#rejected-alternatives">Rejected alternatives</a><ul> <li><a class="reference internal" href="#noop-returns-something"><code class="docutils literal notranslate"><span class="pre">noop()</span></code> returns something</a></li> </ul> </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-0559.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>