[Python-checkins] r79670 - in python/branches/py3k: Doc/library/fractions.rst Lib/fractions.py Lib/test/test_fractions.py Misc/NEWS
mark.dickinson
python-checkins at python.org
Sat Apr 3 13:18:53 CEST 2010
Author: mark.dickinson
Date: Sat Apr 3 13:18:52 2010
New Revision: 79670
Log:
Merged revisions 79629 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r79629 | mark.dickinson | 2010-04-02 23:27:36 +0100 (Fri, 02 Apr 2010) | 2 lines
Issue #8294: Allow float and Decimal arguments in Fraction constructor.
........
Modified:
python/branches/py3k/ (props changed)
python/branches/py3k/Doc/library/fractions.rst
python/branches/py3k/Lib/fractions.py
python/branches/py3k/Lib/test/test_fractions.py
python/branches/py3k/Misc/NEWS
Modified: python/branches/py3k/Doc/library/fractions.rst
==============================================================================
--- python/branches/py3k/Doc/library/fractions.rst (original)
+++ python/branches/py3k/Doc/library/fractions.rst Sat Apr 3 13:18:52 2010
@@ -15,17 +15,24 @@
.. class:: Fraction(numerator=0, denominator=1)
Fraction(other_fraction)
+ Fraction(float)
+ Fraction(decimal)
Fraction(string)
- The first version requires that *numerator* and *denominator* are
- instances of :class:`numbers.Rational` and returns a new
- :class:`Fraction` instance with value ``numerator/denominator``. If
- *denominator* is :const:`0`, it raises a
- :exc:`ZeroDivisionError`. The second version requires that
- *other_fraction* is an instance of :class:`numbers.Rational` and
- returns an :class:`Fraction` instance with the same value. The
- last version of the constructor expects a string instance. The
- usual form for this string is::
+ The first version requires that *numerator* and *denominator* are instances
+ of :class:`numbers.Rational` and returns a new :class:`Fraction` instance
+ with value ``numerator/denominator``. If *denominator* is :const:`0`, it
+ raises a :exc:`ZeroDivisionError`. The second version requires that
+ *other_fraction* is an instance of :class:`numbers.Rational` and returns a
+ :class:`Fraction` instance with the same value. The next two versions accept
+ either a :class:`float` or a :class:`decimal.Decimal` instance, and return a
+ :class:`Fraction` instance with exactly the same value. Note that due to the
+ usual issues with binary floating-point (see :ref:`tut-fp-issues`), the
+ argument to ``Fraction(1.1)`` is not exactly equal to 11/10, and so
+ ``Fraction(1.1)`` does *not* return ``Fraction(11, 10)`` as one might expect.
+ (But see the documentation for the :meth:`limit_denominator` method below.)
+ The last version of the constructor expects a string or unicode instance.
+ The usual form for this instance is::
[sign] numerator ['/' denominator]
@@ -55,6 +62,13 @@
Fraction(-1, 8)
>>> Fraction('7e-6')
Fraction(7, 1000000)
+ >>> Fraction(2.25)
+ Fraction(9, 4)
+ >>> Fraction(1.1)
+ Fraction(2476979795053773, 2251799813685248)
+ >>> from decimal import Decimal
+ >>> Fraction(Decimal('1.1'))
+ Fraction(11, 10)
The :class:`Fraction` class inherits from the abstract base class
@@ -63,6 +77,10 @@
and should be treated as immutable. In addition,
:class:`Fraction` has the following methods:
+ .. versionchanged:: 3.2
+ The :class:`Fraction` constructor now accepts :class:`float` and
+ :class:`decimal.Decimal` instances.
+
.. method:: from_float(flt)
@@ -70,12 +88,19 @@
value of *flt*, which must be a :class:`float`. Beware that
``Fraction.from_float(0.3)`` is not the same value as ``Fraction(3, 10)``
+ .. note:: From Python 3.2 onwards, you can also construct a
+ :class:`Fraction` instance directly from a :class:`float`.
+
.. method:: from_decimal(dec)
This class method constructs a :class:`Fraction` representing the exact
value of *dec*, which must be a :class:`decimal.Decimal` instance.
+ .. note:: From Python 3.2 onwards, you can also construct a
+ :class:`Fraction` instance directly from a :class:`decimal.Decimal`
+ instance.
+
.. method:: limit_denominator(max_denominator=1000000)
@@ -90,10 +115,12 @@
or for recovering a rational number that's represented as a float:
>>> from math import pi, cos
- >>> Fraction.from_float(cos(pi/3))
+ >>> Fraction(cos(pi/3))
Fraction(4503599627370497, 9007199254740992)
- >>> Fraction.from_float(cos(pi/3)).limit_denominator()
+ >>> Fraction(cos(pi/3)).limit_denominator()
Fraction(1, 2)
+ >>> Fraction(1.1).limit_denominator()
+ Fraction(11, 10)
.. method:: __floor__()
Modified: python/branches/py3k/Lib/fractions.py
==============================================================================
--- python/branches/py3k/Lib/fractions.py (original)
+++ python/branches/py3k/Lib/fractions.py Sat Apr 3 13:18:52 2010
@@ -3,6 +3,7 @@
"""Fraction, infinite-precision, real numbers."""
+from decimal import Decimal
import math
import numbers
import operator
@@ -41,13 +42,21 @@
class Fraction(numbers.Rational):
"""This class implements rational numbers.
- Fraction(8, 6) will produce a rational number equivalent to
- 4/3. Both arguments must be Integral. The numerator defaults to 0
- and the denominator defaults to 1 so that Fraction(3) == 3 and
- Fraction() == 0.
+ In the two-argument form of the constructor, Fraction(8, 6) will
+ produce a rational number equivalent to 4/3. Both arguments must
+ be Rational. The numerator defaults to 0 and the denominator
+ defaults to 1 so that Fraction(3) == 3 and Fraction() == 0.
- Fraction can also be constructed from strings of the form
- '[-+]?[0-9]+((/|.)[0-9]+)?', optionally surrounded by spaces.
+ Fractions can also be constructed from:
+
+ - numeric strings similar to those accepted by the
+ float constructor (for example, '-2.3' or '1e10')
+
+ - strings of the form '123/456'
+
+ - float and Decimal instances
+
+ - other Rational instances (including integers)
"""
@@ -57,8 +66,32 @@
def __new__(cls, numerator=0, denominator=None):
"""Constructs a Rational.
- Takes a string like '3/2' or '1.5', another Rational, or a
- numerator/denominator pair.
+ Takes a string like '3/2' or '1.5', another Rational instance, a
+ numerator/denominator pair, or a float.
+
+ Examples
+ --------
+
+ >>> Fraction(10, -8)
+ Fraction(-5, 4)
+ >>> Fraction(Fraction(1, 7), 5)
+ Fraction(1, 35)
+ >>> Fraction(Fraction(1, 7), Fraction(2, 3))
+ Fraction(3, 14)
+ >>> Fraction('314')
+ Fraction(314, 1)
+ >>> Fraction('-35/4')
+ Fraction(-35, 4)
+ >>> Fraction('3.1415') # conversion from numeric string
+ Fraction(6283, 2000)
+ >>> Fraction('-47e-2') # string may include a decimal exponent
+ Fraction(-47, 100)
+ >>> Fraction(1.47) # direct construction from float (exact conversion)
+ Fraction(6620291452234629, 4503599627370496)
+ >>> Fraction(2.25)
+ Fraction(9, 4)
+ >>> Fraction(Decimal('1.47'))
+ Fraction(147, 100)
"""
self = super(Fraction, cls).__new__(cls)
@@ -69,6 +102,19 @@
self._denominator = numerator.denominator
return self
+ elif isinstance(numerator, float):
+ # Exact conversion from float
+ value = Fraction.from_float(numerator)
+ self._numerator = value._numerator
+ self._denominator = value._denominator
+ return self
+
+ elif isinstance(numerator, Decimal):
+ value = Fraction.from_decimal(numerator)
+ self._numerator = value._numerator
+ self._denominator = value._denominator
+ return self
+
elif isinstance(numerator, str):
# Handle construction from strings.
m = _RATIONAL_FORMAT.match(numerator)
Modified: python/branches/py3k/Lib/test/test_fractions.py
==============================================================================
--- python/branches/py3k/Lib/test/test_fractions.py (original)
+++ python/branches/py3k/Lib/test/test_fractions.py Sat Apr 3 13:18:52 2010
@@ -12,6 +12,11 @@
F = fractions.Fraction
gcd = fractions.gcd
+# decorator for skipping tests on non-IEEE 754 platforms
+requires_IEEE_754 = unittest.skipUnless(
+ float.__getformat__("double").startswith("IEEE"),
+ "test requires IEEE 754 doubles")
+
class DummyFloat(object):
"""Dummy float class for testing comparisons with Fractions"""
@@ -130,13 +135,33 @@
self.assertRaisesMessage(ZeroDivisionError, "Fraction(12, 0)",
F, 12, 0)
- self.assertRaises(TypeError, F, 1.5)
self.assertRaises(TypeError, F, 1.5 + 3j)
self.assertRaises(TypeError, F, "3/2", 3)
self.assertRaises(TypeError, F, 3, 0j)
self.assertRaises(TypeError, F, 3, 1j)
+ @requires_IEEE_754
+ def testInitFromFloat(self):
+ self.assertEquals((5, 2), _components(F(2.5)))
+ self.assertEquals((0, 1), _components(F(-0.0)))
+ self.assertEquals((3602879701896397, 36028797018963968),
+ _components(F(0.1)))
+ self.assertRaises(TypeError, F, float('nan'))
+ self.assertRaises(TypeError, F, float('inf'))
+ self.assertRaises(TypeError, F, float('-inf'))
+
+ def testInitFromDecimal(self):
+ self.assertEquals((11, 10),
+ _components(F(Decimal('1.1'))))
+ self.assertEquals((7, 200),
+ _components(F(Decimal('3.5e-2'))))
+ self.assertEquals((0, 1),
+ _components(F(Decimal('.000e20'))))
+ self.assertRaises(TypeError, F, Decimal('nan'))
+ self.assertRaises(TypeError, F, Decimal('snan'))
+ self.assertRaises(TypeError, F, Decimal('inf'))
+ self.assertRaises(TypeError, F, Decimal('-inf'))
def testFromString(self):
self.assertEquals((5, 1), _components(F("5")))
Modified: python/branches/py3k/Misc/NEWS
==============================================================================
--- python/branches/py3k/Misc/NEWS (original)
+++ python/branches/py3k/Misc/NEWS Sat Apr 3 13:18:52 2010
@@ -301,6 +301,9 @@
Library
-------
+- Issue #8294: The Fraction constructor now accepts Decimal and float
+ instances directly.
+
- Issue #7279: Comparisons involving a Decimal signaling NaN now
signal InvalidOperation instead of returning False. (Comparisons
involving a quiet NaN are unchanged.) Also, Decimal quiet NaNs
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