S
Steven D'Aprano
What's obvious to you and what's obvious to the Python VM are not
necessarily the same thing. I believe you are worrying about the wrong
thing. (BTW, I think your earlier decorator had a bug, in that it failed
to define __ne__ but then called "self != other".) My tests suggest that
relying on __cmp__ is nearly three times *slower* than your decorated
class, and around four times slower than defining all the rich
comparisons directly:
$ python comparisons.py
Testing FractionCmp... 37.4376080036
Testing FractionRichCmpDirect... 9.83379387856
Testing FractionRichCmpIndirect... 16.152534008
Testing FractionDecoratored... 13.2626030445
Test code follows. If I've made an error, please let me know.
[comparisons.py]
from __future__ import division
def totally_ordered(cls):
# Define total ordering in terms of __eq__ and __lt__ only.
if not hasattr(cls, '__ne__'):
def ne(self, other):
return not self == other
cls.__ne__ = ne
if not hasattr(cls, '__gt__'):
def gt(self, other):
return not (self < other or self == other)
cls.__gt__ = gt
if not hasattr(cls, '__ge__'):
def ge(self, other):
return not (self < other)
cls.__ge__ = ge
if not hasattr(cls, '__le__'):
def le(self, other):
return (self < other or self == other)
cls.__le__ = le
return cls
class AbstractFraction:
def __init__(self, num, den=1):
if self.__class__ is AbstractFraction:
raise TypeError("abstract base class, do not instantiate")
assert den > 0, "denomintator must be > 0"
self.num = num
self.den = den
def __float__(self):
return self.num/self.den
class FractionCmp(AbstractFraction):
def __cmp__(self, other):
return cmp(self.num*other.den, self.den*other.num)
class FractionRichCmpDirect(AbstractFraction):
def __eq__(self, other):
return (self.num*other.den) == (self.den*other.num)
def __ne__(self, other):
return (self.num*other.den) != (self.den*other.num)
def __lt__(self, other):
return (self.num*other.den) < (self.den*other.num)
def __le__(self, other):
return (self.num*other.den) <= (self.den*other.num)
def __gt__(self, other):
return (self.num*other.den) > (self.den*other.num)
def __ge__(self, other):
return (self.num*other.den) >= (self.den*other.num)
class FractionRichCmpIndirect(AbstractFraction):
def __cmp__(self, other):
return cmp(self.num*other.den, self.den*other.num)
def __eq__(self, other):
return self.__cmp__(other) == 0
def __ne__(self, other):
return self.__cmp__(other) != 0
def __lt__(self, other):
return self.__cmp__(other) < 0
def __le__(self, other):
return self.__cmp__(other) <= 0
def __gt__(self, other):
return self.__cmp__(other) > 0
def __ge__(self, other):
return self.__cmp__(other) >= 0
class FractionDecoratored(AbstractFraction):
def __eq__(self, other):
return self.num*other.den == self.den*other.num
def __lt__(self, other):
return self.num*other.den < self.den*other.num
FractionDecoratored = totally_ordered(FractionDecoratored)
def test_suite(small, big):
assert small < big
assert small <= big
assert not (small > big)
assert not (small >= big)
assert small != big
assert not (small == big)
from timeit import Timer
test = 'test_suite(p, q)'
setup = '''from __main__ import %s as frac
from __main__ import test_suite
p = frac(1, 2)
q = frac(4, 5)
assert float(p) < float(q)'''
for cls in [FractionCmp, FractionRichCmpDirect, FractionRichCmpIndirect,
FractionDecoratored]:
t = Timer(test, setup % cls.__name__)
print "Testing %s..." % cls.__name__,
best = min(t.repeat())
print best
[end comparisons.py]