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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 321 – Date/Time Parsing and Formatting | peps.python.org</title> <link rel="shortcut icon" href="../_static/py.png"> <link rel="canonical" href="https://peps.python.org/pep-0321/"> <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 321 – Date/Time Parsing and Formatting | peps.python.org'> <meta property="og:description" content="Python 2.3 added a number of simple date and time types in the datetime module. 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Kuchling <amk at amk.ca></dd> <dt class="field-even">Status<span class="colon">:</span></dt> <dd class="field-even"><abbr title="Removed from consideration by sponsor or authors">Withdrawn</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">16-Sep-2003</dd> <dt class="field-odd">Python-Version<span class="colon">:</span></dt> <dd class="field-odd">2.4</dd> <dt class="field-even">Post-History<span class="colon">:</span></dt> <dd class="field-even"><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="#input-formats">Input Formats</a></li> <li><a class="reference internal" href="#generic-input-parsing">Generic Input Parsing</a></li> <li><a class="reference internal" href="#output-formats">Output Formats</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>Python 2.3 added a number of simple date and time types in the <code class="docutils literal notranslate"><span class="pre">datetime</span></code> module. There’s no support for parsing strings in various formats and returning a corresponding instance of one of the types. This PEP proposes adding a family of predefined parsing function for several commonly used date and time formats, and a facility for generic parsing.</p> <p>The types provided by the <code class="docutils literal notranslate"><span class="pre">datetime</span></code> module all have <code class="docutils literal notranslate"><span class="pre">.isoformat()</span></code> and <code class="docutils literal notranslate"><span class="pre">.ctime()</span></code> methods that return string representations of a time, and the <code class="docutils literal notranslate"><span class="pre">.strftime()</span></code> method can be used to construct new formats. There are a number of additional commonly-used formats that would be useful to have as part of the standard library; this PEP also suggests how to add them.</p> </section> <section id="input-formats"> <h2><a class="toc-backref" href="#input-formats" role="doc-backlink">Input Formats</a></h2> <p>Useful formats to support include:</p> <ul class="simple"> <li><a class="reference external" href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">ISO8601</a></li> <li>ARPA/<span class="target" id="index-0"></span><a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2822.html"><strong>RFC 2822</strong></a></li> <li><a class="reference external" href="http://www.opengroup.org/onlinepubs/007908799/xsh/asctime.html">ctime</a></li> <li>Formats commonly written by humans such as the American “MM/DD/YYYY”, the European “YYYY/MM/DD”, and variants such as “DD-Month-YYYY”.</li> <li>CVS-style or tar-style dates (“tomorrow”, “12 hours ago”, etc.)</li> </ul> <p>XXX The Perl <a class="reference external" href="http://search.cpan.org/author/MUIR/Time-modules-2003.0211/lib/Time/ParseDate.pm">ParseDate.pm</a> module supports many different input formats, both absolute and relative. Should we try to support them all?</p> <p>Options:</p> <ol class="arabic"> <li>Add functions to the <code class="docutils literal notranslate"><span class="pre">datetime</span></code> module:<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">datetime</span> <span class="n">d</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">parse_iso8601</span><span class="p">(</span><span class="s2">"2003-09-15T10:34:54"</span><span class="p">)</span> </pre></div> </div> </li> <li>Add class methods to the various types. There are already various class methods such as <code class="docutils literal notranslate"><span class="pre">.now()</span></code>, so this would be pretty natural.:<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">datetime</span> <span class="n">d</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">date</span><span class="o">.</span><span class="n">parse_iso8601</span><span class="p">(</span><span class="s2">"2003-09-15T10:34:54"</span><span class="p">)</span> </pre></div> </div> </li> <li>Add a separate module (possible names: date, date_parse, parse_date) or subpackage (possible names: datetime.parser) containing parsing functions:<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">datetime</span> <span class="n">d</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">parser</span><span class="o">.</span><span class="n">parse_iso8601</span><span class="p">(</span><span class="s2">"2003-09-15T10:34:54"</span><span class="p">)</span> </pre></div> </div> </li> </ol> <p>Unresolved questions:</p> <ul class="simple"> <li>Naming convention to use.</li> <li>What exception to raise on errors? ValueError, or a specialized exception?</li> <li>Should you know what type you’re expecting, or should the parsing figure it out? (e.g. <code class="docutils literal notranslate"><span class="pre">parse_iso8601("yyyy-mm-dd")</span></code> returns a <code class="docutils literal notranslate"><span class="pre">date</span></code> instance, but parsing “yyyy-mm-ddThh:mm:ss” returns a <code class="docutils literal notranslate"><span class="pre">datetime</span></code>.) Should there be an option to signal an error if a time is provided where none is expected, or if no time is provided?</li> <li>Anything special required for I18N? For time zones?</li> </ul> </section> <section id="generic-input-parsing"> <h2><a class="toc-backref" href="#generic-input-parsing" role="doc-backlink">Generic Input Parsing</a></h2> <p>Is a strptime() implementation that returns <code class="docutils literal notranslate"><span class="pre">datetime</span></code> types sufficient?</p> <p>XXX if yes, describe strptime here. Can the existing pure-Python implementation be easily retargeted?</p> </section> <section id="output-formats"> <h2><a class="toc-backref" href="#output-formats" role="doc-backlink">Output Formats</a></h2> <p>Not all input formats need to be supported as output formats, because it’s pretty trivial to get the <code class="docutils literal notranslate"><span class="pre">strftime()</span></code> argument right for simple things such as YYYY/MM/DD. Only complicated formats need to be supported; <span class="target" id="index-1"></span><a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2822.html"><strong>RFC 2822</strong></a> is currently the only one I can think of.</p> <p>Options:</p> <ol class="arabic"> <li>Provide predefined format strings, so you could write this:<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">datetime</span> <span class="n">d</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="p">(</span><span class="o">...</span><span class="p">)</span> <span class="nb">print</span> <span class="n">d</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">RFC2822_FORMAT</span><span class="p">)</span> <span class="c1"># or datetime.RFC2822_FORMAT?</span> </pre></div> </div> </li> <li>Provide new methods on all the objects:<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">d</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="p">(</span><span class="o">...</span><span class="p">)</span> <span class="nb">print</span> <span class="n">d</span><span class="o">.</span><span class="n">rfc822_time</span><span class="p">()</span> </pre></div> </div> </li> </ol> <p>Relevant functionality in other languages includes the <a class="reference external" href="http://www.php.net/date">PHP date</a> function (Python implementation by Simon Willison at <a class="reference external" href="http://simon.incutio.com/archive/2003/10/07/dateInPython">http://simon.incutio.com/archive/2003/10/07/dateInPython</a>)</p> </section> <section id="references"> <h2><a class="toc-backref" href="#references" role="doc-backlink">References</a></h2> <p>Other useful links:</p> <p><a class="reference external" href="http://www.egenix.com/files/python/mxDateTime.html">http://www.egenix.com/files/python/mxDateTime.html</a> <a class="reference external" href="http://ringmaster.arc.nasa.gov/tools/time_formats.html">http://ringmaster.arc.nasa.gov/tools/time_formats.html</a> <a class="reference external" href="http://www.thinkage.ca/english/gcos/expl/b/lib/0tosec.html">http://www.thinkage.ca/english/gcos/expl/b/lib/0tosec.html</a> <a class="reference external" href="https://moin.conectiva.com.br/DateUtil">https://moin.conectiva.com.br/DateUtil</a></p> </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-0321.rst">https://github.com/python/peps/blob/main/peps/pep-0321.rst</a></p> <p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0321.rst">2025-02-01 08:59:27 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="#input-formats">Input Formats</a></li> <li><a class="reference internal" href="#generic-input-parsing">Generic Input Parsing</a></li> <li><a class="reference internal" href="#output-formats">Output Formats</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-0321.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>