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Issue #21136: Avoid unnecessary normalization in Fractions resulting from power and other operations.

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This commit is contained in:
Mark Dickinson 2014-04-05 09:29:00 +01:00
parent 2a32200838
commit 3c286e2e0d
3 changed files with 19 additions and 10 deletions
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23
Lib/fractions.py
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@ -70,7 +70,7 @@ class Fraction(numbers.Rational):
__slots__ = ('_numerator', '_denominator')
# We're immutable, so use __new__ not __init__
def __new__(cls, numerator=0, denominator=None):
def __new__(cls, numerator=0, denominator=None, _normalize=True):
"""Constructs a Rational.
Takes a string like '3/2' or '1.5', another Rational instance, a
@ -165,9 +165,12 @@ class Fraction(numbers.Rational):
if denominator == 0:
raise ZeroDivisionError('Fraction(%s, 0)' % numerator)
g = gcd(numerator, denominator)
self._numerator = numerator // g
self._denominator = denominator // g
if _normalize:
g = gcd(numerator, denominator)
numerator //= g
denominator //= g
self._numerator = numerator
self._denominator = denominator
return self
@classmethod
@ -453,10 +456,12 @@ class Fraction(numbers.Rational):
power = b.numerator
if power >= 0:
return Fraction(a._numerator ** power,
a._denominator ** power)
a._denominator ** power,
_normalize=False)
else:
return Fraction(a._denominator ** -power,
a._numerator ** -power)
a._numerator ** -power,
_normalize=False)
else:
# A fractional power will generally produce an
# irrational number.
@ -480,15 +485,15 @@ class Fraction(numbers.Rational):
def __pos__(a):
"""+a: Coerces a subclass instance to Fraction"""
return Fraction(a._numerator, a._denominator)
return Fraction(a._numerator, a._denominator, _normalize=False)
def __neg__(a):
"""-a"""
return Fraction(-a._numerator, a._denominator)
return Fraction(-a._numerator, a._denominator, _normalize=False)
def __abs__(a):
"""abs(a)"""
return Fraction(abs(a._numerator), a._denominator)
return Fraction(abs(a._numerator), a._denominator, _normalize=False)
def __trunc__(a):
"""trunc(a)"""