129 lines
4.5 KiB
Plaintext
129 lines
4.5 KiB
Plaintext
PEP: 313
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Title: Adding Roman Numeral Literals to Python
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Version: $Revision$
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Last-Modified: $Date$
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Author: Mike Meyer <mwm@mired.org>
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Status: Rejected
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Type: Standards Track
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Content-Type: text/plain
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Created: 01-Apr-2003
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Python-Version: 2.4
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Post-History:
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Abstract
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This PEP (also known as PEP CCCXIII) proposes adding Roman
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numerals as a literal type. It also proposes the new built-in
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function "roman", which converts an object to an integer, then
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converts the integer to a string that is the Roman numeral literal
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equivalent to the integer.
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BDFL Pronouncement
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This PEP is rejected. While the majority of Python users deemed this
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to be a nice-to-have feature, the community was unable to reach a
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consensus on whether nine should be represented as IX, the modern
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form, or VIIII, the classic form. Likewise, no agreement was
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reached on whether MXM or MCMXC would be considered a well-formed
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representation of 1990. A vocal minority of users has also requested
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support for lower-cased numerals for use in (i) powerpoint slides,
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(ii) academic work, and (iii) Perl documentation.
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Rationale
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Roman numerals are used in a number of areas, and adding them to
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Python as literals would make computations in those areas easier.
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For instance, Superbowls are counted with Roman numerals, and many
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older movies have copyright dates in Roman numerals. Further,
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LISP provides a Roman numerals literal package, so adding Roman
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numerals to Python will help ease the LISP-envy sometimes seen in
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comp.lang.python. Besides, the author thinks this is the easiest
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way to get his name on a PEP.
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Syntax for Roman literals
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Roman numeral literals will consist of the characters M, D, C, L,
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X, V and I, and only those characters. They must be in upper
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case, and represent an integer with the following rules:
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1. Except as noted below, they must appear in the order M, D, C,
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L, X, V then I. Each occurrence of each character adds 1000, 500,
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100, 50, 10, 5 and 1 to the value of the literal, respectively.
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2. Only one D, V or L may appear in any given literal.
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3. At most three each of Is, Xs and Cs may appear consecutively
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in any given literal.
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4. A single I may appear immediately to the left of the single V,
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followed by no Is, and adds 4 to the value of the literal.
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5. A single I may likewise appear before the last X, followed by
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no Is or Vs, and adds 9 to the value.
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6. X is to L and C as I is to V and X, except the values are 40
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and 90, respectively.
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7. C is to D and M as I is to V and X, except the values are 400
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and 900, respectively.
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Any literal composed entirely of M, D, C, L, X, V and I characters
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that does not follow this format will raise a syntax error,
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because explicit is better than implicit.
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Built-In "roman" Function
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The new built-in function "roman" will aide the translation from
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integers to Roman numeral literals. It will accept a single
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object as an argument, and return a string containing the literal
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of the same value. If the argument is not an integer or a
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rational (see PEP 239 [1]) it will passed through the existing
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built-in "int" to obtain the value. This may cause a loss of
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information if the object was a float. If the object is a
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rational, then the result will be formatted as a rational literal
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(see PEP 240 [2]) with the integers in the string being Roman
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numeral literals.
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Compatibility Issues
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No new keywords are introduced by this proposal. Programs that
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use variable names that are all upper case and contain only the
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characters M, D, C, L, X, V and I will be affected by the new
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literals. These programs will now have syntax errors when those
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variables are assigned, and either syntax errors or subtle bugs
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when those variables are referenced in expressions. Since such
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variable names violate PEP 8 [3], the code is already broken, it
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just wasn't generating exceptions. This proposal corrects that
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oversight in the language.
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References
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[1] PEP 239, Adding a Rational Type to Python
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http://www.python.org/dev/peps/pep-0239/
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[2] PEP 240, Adding a Rational Literal to Python
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http://www.python.org/dev/peps/pep-0240/
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[3] PEP 8, Style Guide for Python Code
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http://www.python.org/dev/peps/pep-0008/
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Copyright
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This document has been placed in the public domain.
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Local Variables:
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