gh-72902: speedup Fraction.from_Decimal/float in typical cases

Author: skirpichev

Lib/fractions.py

@@ -335,23 +335,23 @@ def from_float(cls, f):
         Beware that Fraction.from_float(0.3) != Fraction(3, 10).
 
         """
-        if isinstance(f, numbers.Integral):
+        if not isinstance(f, float):
+            if not isinstance(f, numbers.Integral):
+                raise TypeError("%s.from_float() only takes floats, not %r (%s)" %
+                                (cls.__name__, f, type(f).__name__))
             return cls(f)
-        elif not isinstance(f, float):
-            raise TypeError("%s.from_float() only takes floats, not %r (%s)" %
-                            (cls.__name__, f, type(f).__name__))
         return cls._from_coprime_ints(*f.as_integer_ratio())
 
     @classmethod
     def from_decimal(cls, dec):
         """Converts a finite Decimal instance to a rational number, exactly."""
         from decimal import Decimal
-        if isinstance(dec, numbers.Integral):
-            dec = Decimal(int(dec))
-        elif not isinstance(dec, Decimal):
-            raise TypeError(
-                "%s.from_decimal() only takes Decimals, not %r (%s)" %
-                (cls.__name__, dec, type(dec).__name__))
+        if not isinstance(dec, Decimal):
+            if not isinstance(dec, numbers.Integral):
+                raise TypeError(
+                    "%s.from_decimal() only takes Decimals, not %r (%s)" %
+                    (cls.__name__, dec, type(dec).__name__))
+            dec = int(dec)
         return cls._from_coprime_ints(*dec.as_integer_ratio())
 
     @classmethod

Misc/NEWS.d/next/Library/2025-05-01-16-44-16.gh-issue-72902.19qwJW.rst

@@ -0,0 +1,3 @@
+Optimize (~x1.40-50 speedup) :meth:`fractions.Fraction.from_Decimal` and
+:meth:`fractions.Fraction.from_float` for :class:`~decimal.Decimal` and
+:class:`float` inputs, respectively.  Patch by Sergey B Kirpichev.