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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 313 – Adding Roman Numeral Literals to Python | peps.python.org</title> <link rel="shortcut icon" href="../_static/py.png"> <link rel="canonical" href="https://peps.python.org/pep-0313/"> <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 313 – Adding Roman Numeral Literals to Python | peps.python.org'> <meta property="og:description" content="This PEP (also known as PEP CCCXIII) proposes adding Roman numerals as a literal type. 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It also proposes the new built-in function “roman”, which converts an object to an integer, then converts the integer to a string that is the Roman numeral literal equivalent to the integer.</p> </section> <section id="bdfl-pronouncement"> <h2><a class="toc-backref" href="#bdfl-pronouncement" role="doc-backlink">BDFL Pronouncement</a></h2> <p>This PEP is rejected. While the majority of Python users deemed this to be a nice-to-have feature, the community was unable to reach a consensus on whether nine should be represented as IX, the modern form, or VIIII, the classic form. Likewise, no agreement was reached on whether MXM or MCMXC would be considered a well-formed representation of 1990. A vocal minority of users has also requested support for lower-cased numerals for use in (i) powerpoint slides, (ii) academic work, and (iii) Perl documentation.</p> </section> <section id="rationale"> <h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2> <p>Roman numerals are used in a number of areas, and adding them to Python as literals would make computations in those areas easier. For instance, Super Bowls are counted with Roman numerals, and many older movies have copyright dates in Roman numerals. Further, LISP provides a Roman numerals literal package, so adding Roman numerals to Python will help ease the LISP-envy sometimes seen in comp.lang.python. Besides, the author thinks this is the easiest way to get his name on a PEP.</p> </section> <section id="syntax-for-roman-literals"> <h2><a class="toc-backref" href="#syntax-for-roman-literals" role="doc-backlink">Syntax for Roman literals</a></h2> <p>Roman numeral literals will consist of the characters M, D, C, L, X, V and I, and only those characters. They must be in upper case, and represent an integer with the following rules:</p> <ol class="arabic simple"> <li>Except as noted below, they must appear in the order M, D, C, L, X, V then I. Each occurrence of each character adds 1000, 500, 100, 50, 10, 5 and 1 to the value of the literal, respectively.</li> <li>Only one D, V or L may appear in any given literal.</li> <li>At most three each of Is, Xs and Cs may appear consecutively in any given literal.</li> <li>A single I may appear immediately to the left of the single V, followed by no Is, and adds 4 to the value of the literal.</li> <li>A single I may likewise appear before the last X, followed by no Is or Vs, and adds 9 to the value.</li> <li>X is to L and C as I is to V and X, except the values are 40 and 90, respectively.</li> <li>C is to D and M as I is to V and X, except the values are 400 and 900, respectively.</li> </ol> <p>Any literal composed entirely of M, D, C, L, X, V and I characters that does not follow this format will raise a syntax error, because explicit is better than implicit.</p> </section> <section id="built-in-roman-function"> <h2><a class="toc-backref" href="#built-in-roman-function" role="doc-backlink">Built-In “roman” Function</a></h2> <p>The new built-in function “roman” will aide the translation from integers to Roman numeral literals. It will accept a single object as an argument, and return a string containing the literal of the same value. If the argument is not an integer or a rational (see <a class="pep reference internal" href="../pep-0239/" title="PEP 239 – Adding a Rational Type to Python">PEP 239</a>) it will passed through the existing built-in “int” to obtain the value. This may cause a loss of information if the object was a float. If the object is a rational, then the result will be formatted as a rational literal (see <a class="pep reference internal" href="../pep-0240/" title="PEP 240 – Adding a Rational Literal to Python">PEP 240</a>) with the integers in the string being Roman numeral literals.</p> </section> <section id="compatibility-issues"> <h2><a class="toc-backref" href="#compatibility-issues" role="doc-backlink">Compatibility Issues</a></h2> <p>No new keywords are introduced by this proposal. Programs that use variable names that are all upper case and contain only the characters M, D, C, L, X, V and I will be affected by the new literals. These programs will now have syntax errors when those variables are assigned, and either syntax errors or subtle bugs when those variables are referenced in expressions. Since such variable names violate <a class="pep reference internal" href="../pep-0008/" title="PEP 8 – Style Guide for Python Code">PEP 8</a>, the code is already broken, it just wasn’t generating exceptions. This proposal corrects that oversight in the language.</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-0313.rst">https://github.com/python/peps/blob/main/peps/pep-0313.rst</a></p> <p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0313.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="#bdfl-pronouncement">BDFL Pronouncement</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#syntax-for-roman-literals">Syntax for Roman literals</a></li> <li><a class="reference internal" href="#built-in-roman-function">Built-In “roman” Function</a></li> <li><a class="reference internal" href="#compatibility-issues">Compatibility Issues</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-0313.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>