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

[skirpichev]

• Issue: Fractions instantiation revisited #72902

[skirpichev]

Benchmark	ref	patch	patch2
Fraction.from_decimal(1)	15.5 us	6.59 us: 2.35x faster	10.4 us: 1.49x faster
Fraction.from_decimal(myint)	16.3 us	11.4 us: 1.43x faster	10.8 us: 1.51x faster
Fraction.from_decimal(Decimal('1'))	10.9 us	7.94 us: 1.37x faster	7.88 us: 1.38x faster
Fraction.from_float(1)	7.06 us	4.25 us: 1.66x faster	7.68 us: 1.09x slower
Fraction.from_float(myint)	8.87 us	9.92 us: 1.12x slower	9.36 us: 1.06x slower
Fraction.from_float(1.1)	7.37 us	4.68 us: 1.57x faster	4.68 us: 1.58x faster
Geometric mean	(ref)	1.49x faster	1.27x faster

Here patch2 is the current version. v1 had a hack to check isinstance(op, (int, Integral)) instead.

# bench.py
import pyperf
from fractions import Fraction as F
from decimal import Decimal as D
from numbers import Integral

runner = pyperf.Runner()
s = 'Fraction.from_decimal'
f = F.from_decimal
class myint:
    numerator = 123
    denominator = 1
    def __int__(self):
        return 123
    def __repr__(self):
        return "myint"
Integral.register(myint)
for v in [1, myint(), D(1)]:
    r = s + '(' + repr(v) + ')'
    runner.bench_func(r, f, v)
s = 'Fraction.from_float'
f = F.from_float
for v in [1, myint(), 1.1]:
    r = s + '(' + repr(v) + ')'
    runner.bench_func(r, f, v)

diff --git a/Lib/fractions.py b/Lib/fractions.py
index fa722589fb..d7887af9f8 100644
--- a/Lib/fractions.py
+++ b/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, (int, 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, (int, 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