[Python-Dev] performance of {} versus dict()

[Chris Angelico]

On Thu, Nov 15, 2012 at 1:28 PM, Stephen J. Turnbull <stephen at xemacs.org> wrote:
> Chris Angelico writes:
>
>  > >>> {"a":1}+{"b":2}
>
>  > It would make sense for this to result in {"a":1,"b":2}.
>
> The test is not "does this sometimes make sense?"  It's "does this
> ever result in nonsense, and if so, do we care?"
>
> Here, addition is usually commutative.  Should {'a':1}+{'a':2} be the
> same as, or different from, {'a':2}+{'a':1}, or should it be an error?

>>> "a"+"b"
'ab'
>>> "b"+"a"
'ba'

I would say that the two dictionary examples are equally allowed to
give different results - that they should be equivalent to (shallow)
copy followed by update(), but possibly more efficiently.

ChrisA