gh-82017: Support as_integer_ratio() in the Fraction constructor

Doc/library/fractions.rst

@@ -18,24 +18,26 @@ A Fraction instance can be constructed from a pair of integers, from
 another rational number, or from a string.
 
 .. class:: Fraction(numerator=0, denominator=1)
- Fraction(other_fraction)
- Fraction(float)
- Fraction(decimal)
+ Fraction(number)
  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 ``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
+ raises a :exc:`ZeroDivisionError`.
+
+ The second version requires that
+ *number* is an instance of :class:`numbers.Rational` or is an instance
+ of :class:`numbers.Number` and has the :meth:`~as_integer_ratio` method
+ (this includes :class:`float` and :class:`decimal.Decimal`).
+ It returns 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 last version of the constructor expects a string.
  The usual form for this instance is::
 
  [sign] numerator ['/' denominator]

Doc/whatsnew/3.14.rst

@@ -92,6 +92,13 @@ ast
 Added :func:`ast.compare` for comparing two ASTs.
 (Contributed by Batuhan Taskaya and Jeremy Hylton in :issue:`15987`.)
 
+fractions
+---------
+
+Added support for converting any numbers that have the
+:meth:`!as_integer_ratio` method to a :class:`~fractions.Fraction`.
+(Contributed by Serhiy Storchaka in :gh:`82017`.)
+
 
 
 Optimizations

Lib/fractions.py

@@ -3,7 +3,6 @@
 
 """Fraction, infinite-precision, rational numbers."""
 
-from decimal import Decimal
 import functools
 import math
 import numbers
@@ -244,7 +243,8 @@ def __new__(cls, numerator=0, denominator=None):
  self._denominator = numerator.denominator
  return self
 
- elif isinstance(numerator, (float, Decimal)):
+ elif (isinstance(numerator, numbers.Number) and
+ hasattr(numerator, 'as_integer_ratio')):
  # Exact conversion
  self._numerator, self._denominator = numerator.as_integer_ratio()
  return self

Lib/test/test_fractions.py

@@ -355,6 +355,29 @@ def testInitFromDecimal(self):
  self.assertRaises(OverflowError, F, Decimal('inf'))
  self.assertRaises(OverflowError, F, Decimal('-inf'))
 
+ def testInitFromIntegerRatio(self):
+ class Ratio:
+ def __init__(self, ratio):
+ self._ratio = ratio
+ def as_integer_ratio(self):
+ return self._ratio
+ class RatioNumber(Ratio):
+ pass
+ numbers.Number.register(RatioNumber)
+
+ self.assertEqual((7, 3), _components(F(RatioNumber((7, 3)))))
+ # not a number
+ self.assertRaises(TypeError, F, Ratio((7, 3)))
+ # the type also has an "as_integer_ratio" attribute.
+ self.assertRaises(TypeError, F, RatioNumber)
+ # bad ratio
+ self.assertRaises(TypeError, F, RatioNumber(7))
+ self.assertRaises(ValueError, F, RatioNumber((7,)))
+ self.assertRaises(ValueError, F, RatioNumber((7, 3, 1)))
+ # only single-argument form
+ self.assertRaises(TypeError, F, RatioNumber((3, 7)), 11)
+ self.assertRaises(TypeError, F, 2, RatioNumber((-10, 9)))
+
  def testFromString(self):
  self.assertEqual((5, 1), _components(F("5")))
  self.assertEqual((3, 2), _components(F("3/2")))

Misc/NEWS.d/next/Library/2024-06-08-17-41-11.gh-issue-82017.WpSTGi.rst

@@ -0,0 +1,2 @@
+Added support for converting any numbers that have the
+:meth:`!as_integer_ratio` method to a :class:`~fractions.Fraction`.