[ python-Bugs-1028306 ] date-datetime comparison

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Bugs item #1028306, was opened at 2004-09-14 21:00
Message generated for change (Settings changed) made by rhettinger
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https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1028306&group_id=5470

Category: Python Library
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Donnal Walter (donnal)
>Assigned to: Tim Peters (tim_one)
Summary: date-datetime comparison

Initial Comment:
> I was surprised to discover that
> 
> >>> import datetime
> >>> x = datetime.date(2004, 9, 14)
> >>> y = datetime.datetime(2004, 9, 14, 6, 43, 15)
> >>> print x == y
> True
> 
> How can these two objects be considered equal?

They should not be.  Please open a bug report.  The 
problem is due to that datetime.datetime is a subclass 
of datetime.date:

>>> isinstance(y, datetime.date) True
>>>

and date's comparison implementation believes that 
instances of date subclasses can be compared as if 
they *were* dates.  Indeed, since a datetime.datetime 
is-a datetime.date, it's a bit hard to see why that 
shouldn't be allowed, and offhand I don't know of a 
principled way to fix this without breaking existing code 
that compares instances of user-defined subclasses of 
datetime.date to instances of datetime.date.

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