At Monday 13/11/2006 21:33, [EMAIL PROTECTED] wrote:
I have a class that has, as an attribute, an instance of
datetime.datetime(). I would like to be able to compare my class
directly to instances of datetime.datetime in addition to other
instances of my class. The value used for the comparison in either
case should be the value of the datetime attribute of the class:
from datetime import datetime
class GeneralizedTime(object):
def __init__(self, time=None):
if time is None:
self.datetime = datetime.now()
def __cmp__(self, x):
if isinstance(x, GeneralizedTime):
return cmp(self.datetime, x.datetime)
if isinstance(x, datetime):
return cmp(self.datetime, x)
>>> import datetime
>>>
>>> GeneralizedTime() > datetime.now()
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: can't compare datetime.datetime to GeneralizedTime
This appears to be some braindead code in the datetime class.
You have to provide all the "rich-comparison" methods, and even then,
will never work when a datetime instance is at the left of the comparison.
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
def __eq__(self, other): return self.__cmp__(other)==0
def __ne__(self, other): return self.__cmp__(other)!=0
When the rich comparison methods raise NotImplementedError, the
comparison logic inside the interpreter tries reversing the operands.
But datetime objects don't do that, they raise TypeError, thus
preventing the operand reversing. So any comparison with datetime on
the left and your GeneralizedTime on the right side will fail.
If nobody has an explanation on *why* datetime does this, I'd say it's a bug.
--
Gabriel Genellina
Softlab SRL
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