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<h1 class="page-title">PEP 217 – Display Hook for Interactive Use</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">Moshe Zadka <moshez at zadka.site.co.il></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abbr title="Accepted and implementation complete, or no longer active">Final</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">31-Jul-2000</dd>
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<dt class="field-odd">Python-Version<span class="colon">:</span></dt>
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<dd class="field-odd">2.1</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="#interface">Interface</a></li>
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<li><a class="reference internal" href="#solution">Solution</a></li>
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<li><a class="reference internal" href="#jython-issues">Jython Issues</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>Python’s interactive mode is one of the implementation’s great
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strengths – being able to write expressions on the command line
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and get back a meaningful output. However, the output function
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cannot be all things to all people, and the current output
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function too often falls short of this goal. This PEP describes a
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way to provides alternatives to the built-in display function in
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Python, so users will have control over the output from the
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interactive interpreter.</p>
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</section>
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<section id="interface">
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<h2><a class="toc-backref" href="#interface" role="doc-backlink">Interface</a></h2>
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<p>The current Python solution has worked for many users, and this
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should not break it. Therefore, in the default configuration,
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nothing will change in the REPL loop. To change the way the
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interpreter prints interactively entered expressions, users
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will have to rebind <code class="docutils literal notranslate"><span class="pre">sys.displayhook</span></code> to a callable object.
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The result of calling this object with the result of the
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interactively entered expression should be print-able,
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and this is what will be printed on <code class="docutils literal notranslate"><span class="pre">sys.stdout</span></code>.</p>
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</section>
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<section id="solution">
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<h2><a class="toc-backref" href="#solution" role="doc-backlink">Solution</a></h2>
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<p>The bytecode <code class="docutils literal notranslate"><span class="pre">PRINT_EXPR</span></code> will call <code class="docutils literal notranslate"><span class="pre">sys.displayhook(POP())</span></code>.
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A <code class="docutils literal notranslate"><span class="pre">displayhook()</span></code> will be added to the sys builtin module, which is
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equivalent to:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>import __builtin__
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def displayhook(o):
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if o is None:
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return
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__builtin__._ = None
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print `o`
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__builtin__._ = o
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</pre></div>
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</div>
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</section>
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<section id="jython-issues">
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<h2><a class="toc-backref" href="#jython-issues" role="doc-backlink">Jython Issues</a></h2>
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<p>The method <code class="docutils literal notranslate"><span class="pre">Py.printResult</span></code> will be similarly changed.</p>
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</section>
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</section>
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<hr class="docutils" />
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<p>Source: <a class="reference external" href="https://github.com/python/peps/blob/main/peps/pep-0217.rst">https://github.com/python/peps/blob/main/peps/pep-0217.rst</a></p>
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<p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0217.rst">2023-09-09 17:39:29 GMT</a></p>
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</article>
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<nav id="pep-sidebar">
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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>
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<li><a class="reference internal" href="#interface">Interface</a></li>
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<li><a class="reference internal" href="#solution">Solution</a></li>
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<li><a class="reference internal" href="#jython-issues">Jython Issues</a></li>
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</ul>
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