python-peps/peps/pep-0313.rst

PEP: 313
Title: Adding Roman Numeral Literals to Python
Version: $Revision$
Last-Modified: $Date$
Author: Mike Meyer <mwm@mired.org>
Status: Rejected
Type: Standards Track
Content-Type: text/x-rst
Created: 01-Apr-2003
Python-Version: 2.4
Post-History:


Abstract
========

This PEP (also known as PEP CCCXIII) proposes adding Roman
numerals as a literal type.  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.


BDFL Pronouncement
==================

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.


Rationale
=========

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.


Syntax for Roman literals
=========================

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:

1.  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.

2.  Only one D, V or L may appear in any given literal.

3.  At most three each of Is, Xs and Cs may appear consecutively
    in any given literal.

4.  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.

5.  A single I may likewise appear before the last X, followed by
    no Is or Vs, and adds 9 to the value.

6.  X is to L and C as I is to V and X, except the values are 40
    and 90, respectively.

7.  C is to D and M as I is to V and X, except the values are 400
    and 900, respectively.

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.


Built-In "roman" Function
=========================

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 :pep:`239`) 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 :pep:`240`) with the integers in the string being Roman
numeral literals.


Compatibility Issues
====================

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 :pep:`8`, the code is already broken, it
just wasn't generating exceptions. This proposal corrects that
oversight in the language.


Copyright
=========

This document has been placed in the public domain.


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