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<h1>Python Enhancement Proposals</h1>
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<h1 class="page-title">PEP 3105 – Make print a function</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">Georg Brandl <georg at python.org></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abbr title="Accepted and implementation complete, or no longer active"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">19-Nov-2006</dd>
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<dt class="field-odd">Python-Version<span class="colon">:</span></dt>
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<dd class="field-odd">3.0</dd>
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<dt class="field-even">Post-History<span class="colon">:</span></dt>
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<dd class="field-even"><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="#rationale">Rationale</a></li>
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<li><a class="reference internal" href="#specification">Specification</a></li>
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<li><a class="reference internal" href="#backwards-compatibility">Backwards Compatibility</a></li>
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<li><a class="reference internal" href="#implementation">Implementation</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>The title says it all – this PEP proposes a new <code class="docutils literal notranslate"><span class="pre">print()</span></code> builtin
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that replaces the <code class="docutils literal notranslate"><span class="pre">print</span></code> statement and suggests a specific signature
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for the new function.</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>The <code class="docutils literal notranslate"><span class="pre">print</span></code> statement has long appeared on lists of dubious language
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features that are to be removed in Python 3000, such as Guido’s “Python
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Regrets” presentation <a class="footnote-reference brackets" href="#id4" id="id1">[1]</a>. As such, the objective of this PEP is not
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new, though it might become much disputed among Python developers.</p>
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<p>The following arguments for a <code class="docutils literal notranslate"><span class="pre">print()</span></code> function are distilled from a
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python-3000 message by Guido himself <a class="footnote-reference brackets" href="#id5" id="id2">[2]</a>:</p>
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<ul class="simple">
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<li><code class="docutils literal notranslate"><span class="pre">print</span></code> is the only application-level functionality that has a
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statement dedicated to it. Within Python’s world, syntax is generally
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used as a last resort, when something <em>can’t</em> be done without help from
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the compiler. Print doesn’t qualify for such an exception.</li>
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<li>At some point in application development one quite often feels the need
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to replace <code class="docutils literal notranslate"><span class="pre">print</span></code> output by something more sophisticated, like
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logging calls or calls into some other I/O library. With a <code class="docutils literal notranslate"><span class="pre">print()</span></code>
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function, this is a straightforward string replacement, today it is
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a mess adding all those parentheses and possibly converting <code class="docutils literal notranslate"><span class="pre">>>stream</span></code>
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style syntax.</li>
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<li>Having special syntax for <code class="docutils literal notranslate"><span class="pre">print</span></code> puts up a much larger barrier for
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evolution, e.g. a hypothetical new <code class="docutils literal notranslate"><span class="pre">printf()</span></code> function is not too
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far fetched when it will coexist with a <code class="docutils literal notranslate"><span class="pre">print()</span></code> function.</li>
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<li>There’s no easy way to convert <code class="docutils literal notranslate"><span class="pre">print</span></code> statements into another call
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if one needs a different separator, not spaces, or none at all.
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Also, there’s no easy way <em>at all</em> to conveniently print objects with
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some other separator than a space.</li>
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<li>If <code class="docutils literal notranslate"><span class="pre">print()</span></code> is a function, it would be much easier to replace it within
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one module (just <code class="docutils literal notranslate"><span class="pre">def</span> <span class="pre">print(*args):...</span></code>) or even throughout a program
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(e.g. by putting a different function in <code class="docutils literal notranslate"><span class="pre">__builtin__.print</span></code>). As it is,
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one can do this by writing a class with a <code class="docutils literal notranslate"><span class="pre">write()</span></code> method and
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assigning that to <code class="docutils literal notranslate"><span class="pre">sys.stdout</span></code> – that’s not bad, but definitely a much
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larger conceptual leap, and it works at a different level than print.</li>
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</ul>
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</section>
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<section id="specification">
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<h2><a class="toc-backref" href="#specification" role="doc-backlink">Specification</a></h2>
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<p>The signature for <code class="docutils literal notranslate"><span class="pre">print()</span></code>, taken from various mailings and recently
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posted on the python-3000 list <a class="footnote-reference brackets" href="#id6" id="id3">[3]</a> is:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">print</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="n">sep</span><span class="o">=</span><span class="s1">' '</span><span class="p">,</span> <span class="n">end</span><span class="o">=</span><span class="s1">'</span><span class="se">\n</span><span class="s1">'</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>A call like:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">print</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">,</span> <span class="n">c</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>will be equivalent to today’s:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">print</span> <span class="o">>></span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">,</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">,</span> <span class="n">c</span>
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</pre></div>
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</div>
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<p>while the optional <code class="docutils literal notranslate"><span class="pre">sep</span></code> and <code class="docutils literal notranslate"><span class="pre">end</span></code> arguments specify what is printed
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between and after the arguments, respectively.</p>
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<p>The <code class="docutils literal notranslate"><span class="pre">softspace</span></code> feature (a semi-secret attribute on files currently
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used to tell print whether to insert a space before the first item)
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will be removed. Therefore, there will not be a direct translation for
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today’s:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">print</span> <span class="s2">"a"</span><span class="p">,</span>
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<span class="nb">print</span>
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</pre></div>
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</div>
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<p>which will not print a space between the <code class="docutils literal notranslate"><span class="pre">"a"</span></code> and the newline.</p>
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</section>
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<section id="backwards-compatibility">
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<h2><a class="toc-backref" href="#backwards-compatibility" role="doc-backlink">Backwards Compatibility</a></h2>
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<p>The changes proposed in this PEP will render most of today’s <code class="docutils literal notranslate"><span class="pre">print</span></code>
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statements invalid. Only those which incidentally feature parentheses
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around all of their arguments will continue to be valid Python syntax
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in version 3.0, and of those, only the ones printing a single
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parenthesized value will continue to do the same thing. For example,
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in 2.x:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span> <span class="p">(</span><span class="s2">"Hello"</span><span class="p">)</span>
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<span class="go">Hello</span>
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<span class="gp">>>> </span><span class="nb">print</span> <span class="p">(</span><span class="s2">"Hello"</span><span class="p">,</span> <span class="s2">"world"</span><span class="p">)</span>
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<span class="go">('Hello', 'world')</span>
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</pre></div>
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</div>
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<p>whereas in 3.0:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span> <span class="p">(</span><span class="s2">"Hello"</span><span class="p">)</span>
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<span class="go">Hello</span>
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<span class="gp">>>> </span><span class="nb">print</span> <span class="p">(</span><span class="s2">"Hello"</span><span class="p">,</span> <span class="s2">"world"</span><span class="p">)</span>
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<span class="go">Hello world</span>
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</pre></div>
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</div>
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<p>Luckily, as it is a statement in Python 2, <code class="docutils literal notranslate"><span class="pre">print</span></code> can be detected
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and replaced reliably and non-ambiguously by an automated tool, so
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there should be no major porting problems (provided someone writes the
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mentioned tool).</p>
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</section>
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<section id="implementation">
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<h2><a class="toc-backref" href="#implementation" role="doc-backlink">Implementation</a></h2>
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<p>The proposed changes were implemented in the Python 3000 branch in the
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Subversion revisions 53685 to 53704. Most of the legacy code in the
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library has been converted too, but it is an ongoing effort to catch
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every print statement that may be left in the distribution.</p>
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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="id4" role="doc-footnote">
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<dt class="label" id="id4">[<a href="#id1">1</a>]</dt>
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<dd><a class="reference external" href="http://legacy.python.org/doc/essays/ppt/regrets/PythonRegrets.pdf">http://legacy.python.org/doc/essays/ppt/regrets/PythonRegrets.pdf</a></aside>
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<aside class="footnote brackets" id="id5" role="doc-footnote">
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<dt class="label" id="id5">[<a href="#id2">2</a>]</dt>
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<dd>Replacement for print in Python 3.0 (Guido van Rossum)
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<a class="reference external" href="https://mail.python.org/pipermail/python-dev/2005-September/056154.html">https://mail.python.org/pipermail/python-dev/2005-September/056154.html</a></aside>
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<aside class="footnote brackets" id="id6" role="doc-footnote">
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<dt class="label" id="id6">[<a href="#id3">3</a>]</dt>
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<dd>print() parameters in py3k (Guido van Rossum)
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<a class="reference external" href="https://mail.python.org/pipermail/python-3000/2006-November/004485.html">https://mail.python.org/pipermail/python-3000/2006-November/004485.html</a></aside>
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</aside>
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||
</section>
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||
<section id="copyright">
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||
<h2><a class="toc-backref" href="#copyright" role="doc-backlink">Copyright</a></h2>
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||
<p>This document has been placed in the public domain.</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-3105.rst">https://github.com/python/peps/blob/main/peps/pep-3105.rst</a></p>
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||
<p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-3105.rst">2023-09-09 17:39:29 GMT</a></p>
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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="#rationale">Rationale</a></li>
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<li><a class="reference internal" href="#specification">Specification</a></li>
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<li><a class="reference internal" href="#backwards-compatibility">Backwards Compatibility</a></li>
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<li><a class="reference internal" href="#implementation">Implementation</a></li>
|
||
<li><a class="reference internal" href="#references">References</a></li>
|
||
<li><a class="reference internal" href="#copyright">Copyright</a></li>
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||
</ul>
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<br>
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<a id="source" href="https://github.com/python/peps/blob/main/peps/pep-3105.rst">Page Source (GitHub)</a>
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