On 2009-08-26 20:00 PM, Jan Kaliszewski wrote:
27-08-2009 o 00:48:33 Robert Kern <robert.k...@gmail.com> wrote:
On 2009-08-26 17:16 PM, RunThePun wrote:
I'd like to build a database wrapper using DictMixin and allow items
to be appended by my own code. The problem is += is always understood
as setitem and getitem plainly.
d = MyDict()
d['a'] = 1
# this is the problem code that's I'd like to override. It's always
setitem('a', getitem('a') + 3)
d['a'] += 3
# i wanted to do something like my own 'appenditem' function which for
example could be useful if getitem is an expensive operation which can
be avoided.
I hope that was clear enough of a request, it's really late at night
here...
I'm sorry, this is just part of the syntax of Python. You cannot
override it.
Though
d['a'] = 3
is equivalent to:
d.__setitem__('a', 3)
The
d['a'] += 3
*is not* equivalent to:
d.__setitem__('a', d.__getitem__('a') + 3)
*but is* equivalent to:
d.__getitem__('a').__iadd__(3)
Then you can override __getitem__() of MyDict in such a way that it
returns prepared (wrapped) object with overriden __iadd__() as you
want to.
You could, but then you will almost certainly run into problems using the
wrapped object in places that really expect the true object.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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