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gh-72902: speedup Fraction.from_decimal/float in typical cases #133251

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gh-72902: speedup Fraction.from_decimal/float in typical cases #133251

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gh-72902: speedup Fraction.from_Decimal/float in typical cases
skirpichev May 1, 2025
1ea8f6a
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skirpichev May 1, 2025
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20 changes: 10 additions & 10 deletions Lib/fractions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-05-01-16-44-16.gh-issue-72902.19qwJW.rst
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Original file line number Diff line number Diff line change
@@ -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.
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