Oops,

Accidentally went off-list -- here it is:

On Fri, Feb 13, 2015 at 8:32 PM, Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:

Steven D'Aprano wrote:

I think that focusing on the question of "which wins" in the case of duplicate keys, the left or right operand, is not very productive. We can just declare that Python semantics are that the last value seen wins,

Sure we can, but that's something to be learned. It's
not going to be obvious to everyone.

no -- but some things are more obvious to more people than others.

dict1 + dict2

being the same as

dict1.update(dict2)

Is pretty easy to explain, and probably the most likely to be intuitively obvious to the most people.

It might be interesting to put a poll on a more general list:

What do you think the result of :

dict1 = {'a':1, 'b':2}

dict2 = {'c':3, 'b':4}

dict3 = dict1 + dict2

to be?

And see what shakes out with a mixture of newbies and more experienced pythoneers think.

This is a pretty classic usability issue -- "intuitive" means "works like one expects" , but everyone expects different things, so different things are intuitive to different people. So often there is NO ONE thing that is most intuitive to everyone.

But the only way to know is some usability testing.

-Chris

Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
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