PEP 239, Adding a Rational Type to Python, Moshe Zadka

[checking in for Moshe, after editorial, spell check, and formatting
passes by Barry]

pep-0239.txt

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+PEP: 239
+Title: Adding a Rational Type to Python
+Version: $Revision$
+Author: pep@zadka.site.co.il (Moshe Zadka)
+Status: Draft
+Type: Standards Track
+Created: 11-Mar-2001
+Python-Version: 2.2
+Post-History:
+
+
+Abstract
+
+    Python has no numeric type with the semantics of an unboundedly
+    precise rational number.  This proposal explains the semantics of
+    such a type, and suggests builtin functions and literals to
+    support such a type.  This PEP suggests no literals for rational
+    numbers; that is left for another PEP[1].
+
+
+Rationale
+
+    While sometimes slower and more memory intensive (in general,
+    unboundedly so) rational arithmetic captures more closely the
+    mathematical ideal of numbers, and tends to have behavior which is
+    less surprising to newbies.  Though many Python implementations of
+    rational numbers have been written, none of these exist in the
+    core, or are documented in any way.  This has made them much less
+    accessible to people who are less Python-savvy.
+
+
+RationalType
+
+    There will be a new numeric type added called RationalType.  Its
+    unary operators will do the obvious thing.  Binary operators will
+    coerce integers and long integers to rationals, and rationals to
+    floats and complexes.
+
+    The following attributes will be supported: .numerator and
+    .denominator.  The language definition will not define these other
+    then that:
+
+        r.denominator * r == r.numerator
+
+    In particular, no guarantees are made regarding the GCD or the
+    sign of the denominator, even though in the proposed
+    implementation, the GCD is always 1 and the denominator is always
+    positive.
+
+    The method r.trim(max_denominator) will return the closest
+    rational s to r such that abs(s.denominator) <= max_denominator.
+
+
+The rational() Builtin
+
+    This function will have the signature rational(n, d=1).  n and d
+    must both be integers, long integers or rationals.  A guarantee is
+    made that
+
+        rational(n, d) * d == n
+
+
+References
+
+    [1] PEP 240, Adding a Rational Literal to Python, Zadka,
+        http://python.sourceforge.net/peps/pep-0240.html
+
+
+Copyright
+
+    This document has been placed in the public domain.
+
+
+
+Local Variables:
+mode: indented-text
+indent-tabs-mode: nil
+End: