Mark Dickinson added the comment:
Alexander: can this be closed as wont fix?
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Python tracker rep...@bugs.python.org
http://bugs.python.org/issue2267
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Changes by Alexander Belopolsky alexander.belopol...@gmail.com:
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resolution: - wont fix
status: open - closed
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http://bugs.python.org/issue2267
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Changes by Brett Cannon br...@python.org:
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nosy: -brett.cannon
versions: +Python 3.4 -Python 3.3
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http://bugs.python.org/issue2267
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Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
Note that before r82065, python prototype, now available as Lib/datetime.py had
binary operations implemented to return subclass instances. Here is annotated
pre-r82065 code:
39876 gvanrossum def __add__(self,
Brett Cannon br...@python.org added the comment:
There is a difference between methods and overridden operators (slightly) in
terms of cognitive understanding. I mean creating a new instance from a
timestamp seems like an operation on the object by the object. Addition,
though, seems like a
Mark Dickinson dicki...@gmail.com added the comment:
I had understood that the rule was that alternate constructors should be
classmethods, for consistency with __new__. (Well, except that __new__ is
actually a staticmethod, of course... )
E.g., after class MyDecimal(Decimal): pass,
Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
I would like to take another shot at this. The link in Amaury's closing comment
no longer works, so here is the relevant post:
Returning same type as self for arithmetic in subclasses
Tim Peters tim.peters at gmail.com
Mark Dickinson dicki...@gmail.com added the comment:
If you want to challenge Guido's design decision, I think python-dev would be
the place to do it.
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Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
If you want to challenge Guido's design decision, I think
python-dev would be the place to do it.
Do you have a link supporting that it was Guido's design decision? This
decision must have been made around class/type
Mark Dickinson dicki...@gmail.com added the comment:
Do you have a link [...]
Nope. Just going on Tim's description of it as Guido's decision. I've no
idea of the history, and I don't particularly recall any recent relevant
python-dev discussions.
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New submission from Paul Komkoff [EMAIL PROTECTED]:
The datetime.datetime class overrides some arithmetic operations for it
to be able to add or subtract timedeltas. However, the result of A + B
operation, where A is instance of a subclass of datetime and B is
timedelta instance will be always
Alexander Belopolsky [EMAIL PROTECTED] added the comment:
This is trivial to implement (see attached) and IMHO is a good idea.
The next question, however is whether similar changes should be made to
timedelta arithmetics. Timedelta case is not so clearcut because of the
usual dilemma of what
Paul Komkoff [EMAIL PROTECTED] added the comment:
I just checked the astimezone method - it also does this.
As with timedelta... well, it's not critical for me now but it worth
thinking about :)
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Tracker [EMAIL PROTECTED]
http://bugs.python.org/issue2267
Amaury Forgeot d'Arc [EMAIL PROTECTED] added the comment:
Recently, the similar issue1562 Decimal can't be subclassed useful was
rejected. In the discussion I found a reference to a former post, which
precisely deals with datetime and timedelta:
Alexander Belopolsky [EMAIL PROTECTED] added the comment:
Invoking a subclass's constructor is only an issue when subclass adds
data members. In this case, arithmetic methods need to be overridden.
Note that my patch does not make __add__ and friends invoke subclass'
constructor, only
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