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Several tweaks: add construction from strings and .from_decimal(), change 

__init__ to __new__ to enforce immutability, and remove "rational." from repr
and the parens from str.
This commit is contained in:
Jeffrey Yasskin 2008-01-19 09:56:06 +00:00
parent bf4c7c8c0d
commit 45169fbc80
3 changed files with 142 additions and 17 deletions
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14
Doc/library/rational.rst
View File

@ -15,6 +15,7 @@ Rational number class.
.. class:: Rational(numerator=0, denominator=1)
Rational(other_rational)
Rational(string)
The first version requires that *numerator* and *denominator* are
instances of :class:`numbers.Integral` and returns a new
@ -22,10 +23,12 @@ Rational number class.
*denominator* is :const:`0`, raises a :exc:`ZeroDivisionError`. The
second version requires that *other_rational* is an instance of
:class:`numbers.Rational` and returns an instance of
:class:`Rational` with the same value.
:class:`Rational` with the same value. The third version expects a
string of the form ``[-+]?[0-9]+(/[0-9]+)?``, optionally surrounded
by spaces.
Implements all of the methods and operations from
:class:`numbers.Rational` and is hashable.
:class:`numbers.Rational` and is immutable and hashable.
.. method:: Rational.from_float(flt)
@ -36,6 +39,13 @@ Rational number class.
10)``
.. method:: Rational.from_decimal(dec)
This classmethod constructs a :class:`Rational` representing the
exact value of *dec*, which must be a
:class:`decimal.Decimal`.
.. method:: Rational.__floor__()
Returns the greatest :class:`int` ``<= self``. Will be accessible

68
Lib/rational.py
View File

@ -7,6 +7,7 @@ from __future__ import division
import math
import numbers
import operator
import re
__all__ = ["Rational"]
@ -76,6 +77,10 @@ def _binary_float_to_ratio(x):
return (top, 2 ** -e)
_RATIONAL_FORMAT = re.compile(
r'^\s*(?P<sign>[-+]?)(?P<num>\d+)(?:/(?P<denom>\d+))?\s*$')
class Rational(RationalAbc):
"""This class implements rational numbers.
@ -84,14 +89,37 @@ class Rational(RationalAbc):
and the denominator defaults to 1 so that Rational(3) == 3 and
Rational() == 0.
Rationals can also be constructed from strings of the form
'[-+]?[0-9]+(/[0-9]+)?', optionally surrounded by spaces.
"""
__slots__ = ('_numerator', '_denominator')
def __init__(self, numerator=0, denominator=1):
if (not isinstance(numerator, numbers.Integral) and
isinstance(numerator, RationalAbc) and
denominator == 1):
# We're immutable, so use __new__ not __init__
def __new__(cls, numerator=0, denominator=1):
"""Constructs a Rational.
Takes a string, another Rational, or a numerator/denominator pair.
"""
self = super(Rational, cls).__new__(cls)
if denominator == 1:
if isinstance(numerator, basestring):
# Handle construction from strings.
input = numerator
m = _RATIONAL_FORMAT.match(input)
if m is None:
raise ValueError('Invalid literal for Rational: ' + input)
numerator = int(m.group('num'))
# Default denominator to 1. That's the only optional group.
denominator = int(m.group('denom') or 1)
if m.group('sign') == '-':
numerator = -numerator
elif (not isinstance(numerator, numbers.Integral) and
isinstance(numerator, RationalAbc)):
# Handle copies from other rationals.
other_rational = numerator
numerator = other_rational.numerator
@ -108,10 +136,15 @@ class Rational(RationalAbc):
g = _gcd(numerator, denominator)
self._numerator = int(numerator // g)
self._denominator = int(denominator // g)
return self
@classmethod
def from_float(cls, f):
"""Converts a float to a rational number, exactly."""
"""Converts a finite float to a rational number, exactly.
Beware that Rational.from_float(0.3) != Rational(3, 10).
"""
if not isinstance(f, float):
raise TypeError("%s.from_float() only takes floats, not %r (%s)" %
(cls.__name__, f, type(f).__name__))
@ -119,6 +152,26 @@ class Rational(RationalAbc):
raise TypeError("Cannot convert %r to %s." % (f, cls.__name__))
return cls(*_binary_float_to_ratio(f))
@classmethod
def from_decimal(cls, dec):
"""Converts a finite Decimal instance to a rational number, exactly."""
from decimal import Decimal
if not isinstance(dec, Decimal):
raise TypeError(
"%s.from_decimal() only takes Decimals, not %r (%s)" %
(cls.__name__, dec, type(dec).__name__))
if not dec.is_finite():
# Catches infinities and nans.
raise TypeError("Cannot convert %s to %s." % (dec, cls.__name__))
sign, digits, exp = dec.as_tuple()
digits = int(''.join(map(str, digits)))
if sign:
digits = -digits
if exp >= 0:
return cls(digits * 10 ** exp)
else:
return cls(digits, 10 ** -exp)
@property
def numerator(a):
return a._numerator
@ -129,15 +182,14 @@ class Rational(RationalAbc):
def __repr__(self):
"""repr(self)"""
return ('rational.Rational(%r,%r)' %
(self.numerator, self.denominator))
return ('Rational(%r,%r)' % (self.numerator, self.denominator))
def __str__(self):
"""str(self)"""
if self.denominator == 1:
return str(self.numerator)
else:
return '(%s/%s)' % (self.numerator, self.denominator)
return '%s/%s' % (self.numerator, self.denominator)
def _operator_fallbacks(monomorphic_operator, fallback_operator):
"""Generates forward and reverse operators given a purely-rational

69
Lib/test/test_rational.py
View File

@ -45,6 +45,44 @@ class RationalTest(unittest.TestCase):
self.assertRaises(TypeError, R, 1.5)
self.assertRaises(TypeError, R, 1.5 + 3j)
self.assertRaises(TypeError, R, R(1, 2), 3)
self.assertRaises(TypeError, R, "3/2", 3)
def testFromString(self):
self.assertEquals((5, 1), _components(R("5")))
self.assertEquals((3, 2), _components(R("3/2")))
self.assertEquals((3, 2), _components(R(" \n +3/2")))
self.assertEquals((-3, 2), _components(R("-3/2 ")))
self.assertEquals((3, 2), _components(R(" 03/02 \n ")))
self.assertEquals((3, 2), _components(R(u" 03/02 \n ")))
self.assertRaisesMessage(
ZeroDivisionError, "Rational(3, 0)",
R, "3/0")
self.assertRaisesMessage(
ValueError, "Invalid literal for Rational: 3/",
R, "3/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Rational: 3 /2",
R, "3 /2")
self.assertRaisesMessage(
# Denominators don't need a sign.
ValueError, "Invalid literal for Rational: 3/+2",
R, "3/+2")
self.assertRaisesMessage(
# Imitate float's parsing.
ValueError, "Invalid literal for Rational: + 3/2",
R, "+ 3/2")
self.assertRaisesMessage(
# Only parse fractions, not decimals.
ValueError, "Invalid literal for Rational: 3.2",
R, "3.2")
def testImmutable(self):
r = R(7, 3)
r.__init__(2, 15)
self.assertEquals((7, 3), _components(r))
def testFromFloat(self):
self.assertRaisesMessage(
TypeError, "Rational.from_float() only takes floats, not 3 (int)",
@ -72,6 +110,31 @@ class RationalTest(unittest.TestCase):
TypeError, "Cannot convert nan to Rational.",
R.from_float, nan)
def testFromDecimal(self):
self.assertRaisesMessage(
TypeError,
"Rational.from_decimal() only takes Decimals, not 3 (int)",
R.from_decimal, 3)
self.assertEquals(R(0), R.from_decimal(Decimal("-0")))
self.assertEquals(R(5, 10), R.from_decimal(Decimal("0.5")))
self.assertEquals(R(5, 1000), R.from_decimal(Decimal("5e-3")))
self.assertEquals(R(5000), R.from_decimal(Decimal("5e3")))
self.assertEquals(1 - R(1, 10**30),
R.from_decimal(Decimal("0." + "9" * 30)))
self.assertRaisesMessage(
TypeError, "Cannot convert Infinity to Rational.",
R.from_decimal, Decimal("inf"))
self.assertRaisesMessage(
TypeError, "Cannot convert -Infinity to Rational.",
R.from_decimal, Decimal("-inf"))
self.assertRaisesMessage(
TypeError, "Cannot convert NaN to Rational.",
R.from_decimal, Decimal("nan"))
self.assertRaisesMessage(
TypeError, "Cannot convert sNaN to Rational.",
R.from_decimal, Decimal("snan"))
def testConversions(self):
self.assertTypedEquals(-1, trunc(R(-11, 10)))
self.assertTypedEquals(-2, R(-11, 10).__floor__())
@ -173,7 +236,7 @@ class RationalTest(unittest.TestCase):
self.assertTypedEquals(1.0 + 0j, (1.0 + 0j) ** R(1, 10))
def testMixingWithDecimal(self):
"""Decimal refuses mixed comparisons."""
# Decimal refuses mixed comparisons.
self.assertRaisesMessage(
TypeError,
"unsupported operand type(s) for +: 'Rational' and 'Decimal'",
@ -236,8 +299,8 @@ class RationalTest(unittest.TestCase):
self.assertFalse(R(5, 2) == 2)
def testStringification(self):
self.assertEquals("rational.Rational(7,3)", repr(R(7, 3)))
self.assertEquals("(7/3)", str(R(7, 3)))
self.assertEquals("Rational(7,3)", repr(R(7, 3)))
self.assertEquals("7/3", str(R(7, 3)))
self.assertEquals("7", str(R(7, 1)))
def testHash(self):