[Python-ideas] Adding "+" and "+=" operators to dict

[Florian Bruhin]

* M.-A. Lemburg <mal at egenix.com> [2015-02-12 09:51:22 +0100]:
> However, I don't really see the point in having an operation that
> takes two dictionaries, creates a new empty one and updates this
> with both sides of the operand. It may be theoretically useful,
> but it results in the same poor performance you have in string
> concatenation.
> 
> In applications, you normally just need the update functionality
> for dictionaries. If you do need a copy, you can create a copy
> explicitly - but those cases are usually rare.
> 
> So +1 on the '+=' syntax, -1 on '+' for dicts.

I think it'd be rather confusing if += works but + does not.

Regarding duplicate keys, IMHO only two options make sense:

1) Raise an exception
2) The right-hand side overrides keys in the left-hand side.

I think #1 would prevent many useful cases where + could be used
instead of .update(), so +1 for #2.

Florian

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