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<h1 class="page-title">PEP 336 – Make None Callable</h1>
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<dl class="rfc2822 field-list simple">
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<dt class="field-odd">Author<span class="colon">:</span></dt>
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<dd class="field-odd">Andrew McClelland <eternalsquire at comcast.net></dd>
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<dt class="field-even">Status<span class="colon">:</span></dt>
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<dd class="field-even"><abbr title="Formally declined and will not be accepted">Rejected</abbr></dd>
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<dt class="field-odd">Type<span class="colon">:</span></dt>
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<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>
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<dt class="field-even">Created<span class="colon">:</span></dt>
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<dd class="field-even">28-Oct-2004</dd>
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<dt class="field-odd">Post-History<span class="colon">:</span></dt>
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<dd class="field-odd"><p></p></dd>
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<details><summary>Table of Contents</summary><ul class="simple">
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<li><a class="reference internal" href="#abstract">Abstract</a></li>
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<li><a class="reference internal" href="#bdfl-pronouncement">BDFL Pronouncement</a></li>
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<li><a class="reference internal" href="#motivation">Motivation</a></li>
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<li><a class="reference internal" href="#rationale">Rationale</a></li>
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<li><a class="reference internal" href="#how-to-use">How To Use</a></li>
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<li><a class="reference internal" href="#references">References</a></li>
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<li><a class="reference internal" href="#copyright">Copyright</a></li>
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</ul>
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</details></section>
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<section id="abstract">
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<h2><a class="toc-backref" href="#abstract" role="doc-backlink">Abstract</a></h2>
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<p><code class="docutils literal notranslate"><span class="pre">None</span></code> should be a callable object that when called with any
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arguments has no side effect and returns <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
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</section>
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<section id="bdfl-pronouncement">
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<h2><a class="toc-backref" href="#bdfl-pronouncement" role="doc-backlink">BDFL Pronouncement</a></h2>
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<p>This PEP is rejected. It is considered a feature that <code class="docutils literal notranslate"><span class="pre">None</span></code> raises
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an error when called. The proposal falls short in tests for
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obviousness, clarity, explicitness, and necessity. The provided Switch
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example is nice but easily handled by a simple lambda definition.
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See python-dev discussion on 17 June 2005 <a class="footnote-reference brackets" href="#id2" id="id1">[1]</a>.</p>
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</section>
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<section id="motivation">
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<h2><a class="toc-backref" href="#motivation" role="doc-backlink">Motivation</a></h2>
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<p>To allow a programming style for selectable actions that is more
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in accordance with the minimalistic functional programming goals
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of the Python language.</p>
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</section>
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<section id="rationale">
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<h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2>
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<p>Allow the use of <code class="docutils literal notranslate"><span class="pre">None</span></code> in method tables as a universal no effect
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rather than either (1) checking a method table entry against <code class="docutils literal notranslate"><span class="pre">None</span></code>
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before calling, or (2) writing a local no effect method with
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arguments similar to other functions in the table.</p>
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<p>The semantics would be effectively:</p>
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<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>
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<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>
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<span class="k">pass</span>
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</pre></div>
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</div>
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</section>
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<section id="how-to-use">
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<h2><a class="toc-backref" href="#how-to-use" role="doc-backlink">How To Use</a></h2>
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<p>Before, checking function table entry against <code class="docutils literal notranslate"><span class="pre">None</span></code>:</p>
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<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>
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<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>
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<span class="nb">print</span> <span class="s1">'a'</span>
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<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>
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<span class="nb">print</span> <span class="s1">'b'</span>
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<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>
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<span class="nb">print</span> <span class="s1">'c'</span>
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<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>
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<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>
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<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>
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<span class="mi">3</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">c</span>
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<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>
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<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>
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</pre></div>
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</div>
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<p>Before, using a local no effect method:</p>
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<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>
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<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>
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<span class="nb">print</span> <span class="s1">'a'</span>
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||
<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>
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<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>
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<span class="nb">print</span> <span class="s1">'c'</span>
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<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>
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<span class="k">pass</span>
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<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>
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||
<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>
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<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>
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<span class="mi">3</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">c</span>
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<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>
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</pre></div>
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</div>
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<p>After:</p>
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<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>
|
||
|
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<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>
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<span class="nb">print</span> <span class="s1">'a'</span>
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|
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<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>
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<span class="nb">print</span> <span class="s1">'b'</span>
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|
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<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>
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<span class="nb">print</span> <span class="s1">'c'</span>
|
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|
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<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>
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||
<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>
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<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>
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<span class="mi">3</span> <span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">c</span>
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<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>
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</pre></div>
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</div>
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</section>
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<section id="references">
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<h2><a class="toc-backref" href="#references" role="doc-backlink">References</a></h2>
|
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<aside class="footnote-list brackets">
|
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<aside class="footnote brackets" id="id2" role="doc-footnote">
|
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<dt class="label" id="id2">[<a href="#id1">1</a>]</dt>
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<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>
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</article>
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<h2>Contents</h2>
|
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<ul>
|
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<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>
|
||
|
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<br>
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<a id="source" href="https://github.com/python/peps/blob/main/peps/pep-0336.rst">Page Source (GitHub)</a>
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