bpo-37836: minor fixes

python · jdemeyer · Aug 18, 2019 · Aug 19, 2019 · Aug 25, 2019 · Aug 26, 2019
commit 9c7bdb5e057d990edb07031379efc7edfe19f886
diff --git a/Doc/library/fractions.rst b/Doc/library/fractions.rst
@@ -82,11 +82,12 @@ or from a string.
 
    .. versionchanged:: 3.2
       The :class:`Fraction` constructor now accepts :class:`float` and
-      :class:`decimal.Decimal` instances.
+      :class:`decimal.Decimal` instances as a single argument.
 
    .. versionchanged:: 3.9
       The :class:`Fraction` constructor now accepts any object with
-      ``as_integer_ratio()`` as numerator or denominator.
+      ``as_integer_ratio()`` (in particular also :class:`float` and
+      :class:`decimal.Decimal` instances) as numerator or denominator.
 
 
    .. attribute:: numerator

diff --git a/Lib/fractions.py b/Lib/fractions.py
@@ -66,13 +66,11 @@ def _as_integer_ratio(obj):
     try:
         f = obj.as_integer_ratio
     except AttributeError:
-        pass
+        if isinstance(obj, numbers.Rational):
+            return (obj.numerator, obj.denominator)
     else:
         return f()
 
-    if isinstance(obj, numbers.Rational):
-        return (obj.numerator, obj.denominator)
-
     return NotImplemented
 
 
@@ -82,20 +80,20 @@ class Fraction(numbers.Rational):
     In the two-argument form of the constructor, Fraction(8, 6) will
     produce a rational number equivalent to 4/3. The numerator defaults
     to 0 and the denominator defaults to 1 so that Fraction(3) == 3 and
-    Fraction() == 0.
+    Fraction() == 0. The numerator and denominator can be:
+
+      - objects with an ``as_integer_ratio()`` method (this includes
+        integers, Fractions, floats and Decimal instances)
+
+      - other Rational instances
 
-    Fractions can be constructed from:
+    Fractions can also be constructed from a string (in this case, only
+    a single argument is allowed):
 
       - numeric strings similar to those accepted by the
         float constructor (for example, '-2.3' or '1e10')
 
       - strings of the form '123/456'
-
-      - objects with an ``as_integer_ratio()`` method (this includes
-        float and Decimal instances)
-
-      - other Rational instances (including integers)
-
     """
 
     __slots__ = ('_numerator', '_denominator')

diff --git a/Misc/NEWS.d/next/Library/2019-08-18-22-29-59.bpo-37836.BbvvFm.rst b/Misc/NEWS.d/next/Library/2019-08-18-22-29-59.bpo-37836.BbvvFm.rst
@@ -1,3 +1,3 @@
-When constructing a :class:`fractions.Fraction`, the given numerator (and
-optional denominator) may now be any object with an ``as_integer_ratio``
-method.
+When constructing a :class:`fractions.Fraction`, the given numerator and
+denominator may now be any object with an ``as_integer_ratio`` method.
+This allows for example passing floats for both the numerator and denominator.