On Mar 17, 2010, at 5:02 PM, Greg Ewing wrote:
> Raymond Hettinger wrote:
>
>> Python 3 doesn't need it because it is possible to not give a result
>> at all. Python 2 does need it because we have to give *some*
>> result.
>
> That's not true -- it's possible for comparisons to raise
> an exception in 2.x, and they sometimes do already:
Complex objects do not support __float__. Decimal objects do.
If an object supports __float__, then a float comparison coerces
its other argument via __float__ and the other argument
never gets a chance to raise an exception.
>>> class D:
def __float__(self):
return 3.14
>>> float(D())
3.1400000000000001
>>> float(complex(3.14))
Traceback (most recent call last):
File "<pyshell#14>", line 1, in <module>
float(complex(3.14))
TypeError: can't convert complex to float
>>> D() < 10.0
True
>>> complex(3.14) < 10.0
Traceback (most recent call last):
File "<pyshell#16>", line 1, in <module>
complex(3.14) < 10.0
TypeError: no ordering relation is defined for complex numbers
Raymond
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