pythongh-72902: improve Fraction constructor speed for typical inputs (pythonGH-134320)

This moves abc check for numbers.Rational - down.

Author: skirpichev

Lib/fractions.py

@@ -238,11 +238,6 @@ def __new__(cls, numerator=0, denominator=None):
                 self._denominator = 1
                 return self
 
-            elif isinstance(numerator, numbers.Rational):
-                self._numerator = numerator.numerator
-                self._denominator = numerator.denominator
-                return self
-
             elif (isinstance(numerator, float) or
                   (not isinstance(numerator, type) and
                    hasattr(numerator, 'as_integer_ratio'))):
@@ -278,6 +273,11 @@ def __new__(cls, numerator=0, denominator=None):
                 if m.group('sign') == '-':
                     numerator = -numerator
 
+            elif isinstance(numerator, numbers.Rational):
+                self._numerator = numerator.numerator
+                self._denominator = numerator.denominator
+                return self
+
             else:
                 raise TypeError("argument should be a string or a Rational "
                                 "instance or have the as_integer_ratio() method")

Misc/NEWS.d/next/Library/2025-05-20-11-35-08.gh-issue-72902.jzEI-E.rst

@@ -0,0 +1,2 @@
+Improve speed (x1.1-1.8) of the :class:`~fractions.Fraction` constructor for
+typical inputs (:class:`float`'s, :class:`~decimal.Decimal`'s or strings).