mirror of https://github.com/python/cpython
gh-121797: Add class method Fraction.from_number() (GH-121800)
It is an alternative constructor which only accepts a single numeric argument. Unlike to Fraction.from_float() and Fraction.from_decimal() it accepts any real numbers supported by the standard constructor (int, float, Decimal, Rational numbers, objects with as_integer_ratio()). Unlike to the standard constructor, it does not accept strings.
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@ -166,6 +166,16 @@ another rational number, or from a string.
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instance.
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.. classmethod:: from_number(number)
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Alternative constructor which only accepts instances of
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:class:`numbers.Integral`, :class:`numbers.Rational`,
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:class:`float` or :class:`decimal.Decimal`, and objects with
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the :meth:`!as_integer_ratio` method, but not strings.
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.. versionadded:: 3.14
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.. method:: limit_denominator(max_denominator=1000000)
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Finds and returns the closest :class:`Fraction` to ``self`` that has
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@ -263,6 +263,10 @@ fractions
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:meth:`!as_integer_ratio` method to a :class:`~fractions.Fraction`.
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(Contributed by Serhiy Storchaka in :gh:`82017`.)
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* Add alternative :class:`~fractions.Fraction` constructor
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:meth:`Fraction.from_number() <fractions.Fraction.from_number>`.
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(Contributed by Serhiy Storchaka in :gh:`121797`.)
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functools
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---------
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@ -279,7 +279,8 @@ class Fraction(numbers.Rational):
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numerator = -numerator
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else:
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raise TypeError("argument should be a string or a number")
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raise TypeError("argument should be a string or a Rational "
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"instance or have the as_integer_ratio() method")
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elif type(numerator) is int is type(denominator):
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pass # *very* normal case
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@ -305,6 +306,28 @@ class Fraction(numbers.Rational):
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self._denominator = denominator
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return self
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@classmethod
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def from_number(cls, number):
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"""Converts a finite real number to a rational number, exactly.
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Beware that Fraction.from_number(0.3) != Fraction(3, 10).
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"""
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if type(number) is int:
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return cls._from_coprime_ints(number, 1)
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elif isinstance(number, numbers.Rational):
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return cls._from_coprime_ints(number.numerator, number.denominator)
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elif (isinstance(number, float) or
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(not isinstance(number, type) and
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hasattr(number, 'as_integer_ratio'))):
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return cls._from_coprime_ints(*number.as_integer_ratio())
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else:
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raise TypeError("argument should be a Rational instance or "
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"have the as_integer_ratio() method")
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@classmethod
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def from_float(cls, f):
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"""Converts a finite float to a rational number, exactly.
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@ -283,6 +283,13 @@ numbers.Complex.register(Rect)
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class RectComplex(Rect, complex):
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pass
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class Ratio:
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def __init__(self, ratio):
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self._ratio = ratio
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def as_integer_ratio(self):
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return self._ratio
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class FractionTest(unittest.TestCase):
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def assertTypedEquals(self, expected, actual):
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@ -355,14 +362,9 @@ class FractionTest(unittest.TestCase):
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self.assertRaises(OverflowError, F, Decimal('-inf'))
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def testInitFromIntegerRatio(self):
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class Ratio:
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def __init__(self, ratio):
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self._ratio = ratio
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def as_integer_ratio(self):
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return self._ratio
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self.assertEqual((7, 3), _components(F(Ratio((7, 3)))))
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errmsg = "argument should be a string or a number"
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errmsg = (r"argument should be a string or a Rational instance or "
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r"have the as_integer_ratio\(\) method")
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# the type also has an "as_integer_ratio" attribute.
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self.assertRaisesRegex(TypeError, errmsg, F, Ratio)
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# bad ratio
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@ -388,6 +390,8 @@ class FractionTest(unittest.TestCase):
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pass
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self.assertRaisesRegex(TypeError, errmsg, F, B)
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self.assertRaisesRegex(TypeError, errmsg, F, B())
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self.assertRaises(TypeError, F.from_number, B)
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self.assertRaises(TypeError, F.from_number, B())
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def testFromString(self):
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self.assertEqual((5, 1), _components(F("5")))
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@ -594,6 +598,37 @@ class FractionTest(unittest.TestCase):
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ValueError, "cannot convert NaN to integer ratio",
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F.from_decimal, Decimal("snan"))
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def testFromNumber(self, cls=F):
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def check(arg, numerator, denominator):
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f = cls.from_number(arg)
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self.assertIs(type(f), cls)
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self.assertEqual(f.numerator, numerator)
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self.assertEqual(f.denominator, denominator)
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check(10, 10, 1)
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check(2.5, 5, 2)
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check(Decimal('2.5'), 5, 2)
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check(F(22, 7), 22, 7)
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check(DummyFraction(22, 7), 22, 7)
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check(Rat(22, 7), 22, 7)
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check(Ratio((22, 7)), 22, 7)
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self.assertRaises(TypeError, cls.from_number, 3+4j)
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self.assertRaises(TypeError, cls.from_number, '5/2')
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self.assertRaises(TypeError, cls.from_number, [])
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self.assertRaises(OverflowError, cls.from_number, float('inf'))
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self.assertRaises(OverflowError, cls.from_number, Decimal('inf'))
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# as_integer_ratio not defined in a class
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class A:
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pass
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a = A()
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a.as_integer_ratio = lambda: (9, 5)
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check(a, 9, 5)
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def testFromNumber_subclass(self):
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self.testFromNumber(DummyFraction)
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def test_is_integer(self):
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self.assertTrue(F(1, 1).is_integer())
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self.assertTrue(F(-1, 1).is_integer())
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@ -0,0 +1,2 @@
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Add alternative :class:`~fractions.Fraction` constructor
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:meth:`Fraction.from_number() <fractions.Fraction.from_number>`.
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