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

[Stephen J. Turnbull]

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?