[Python-ideas] PEP: Dict addition and subtraction
INADA Naoki
songofacandy at gmail.com
Mon Mar 4 05:15:14 EST 2019
On Mon, Mar 4, 2019 at 6:52 PM Stefan Behnel <stefan_ml at behnel.de> wrote:
>
> I think the main intentions is to close a gap in the language.
>
> [1,2,3] + [4,5,6]
>
> works for lists and tuples,
>
> {1,2,3} | {4,5,6}
>
> works for sets, but joining two dicts isn't simply
>
> {1:2, 3:4} + {5:6}
>
Operators are syntax borrowed from math.
* Operators are used for concatenate and repeat (Kleene star) in
regular language.
https://en.wikipedia.org/wiki/Regular_language
seq + seq and seq * N are very similar to it, although Python used +
instead of
middle dot (not in ASCII) for concatenate.
* set is directly relating to set in math. | is well known operator for union.
* In case of merging dict, I don't know obvious background in math or
computer science.
So I feel it's very natural that dict don't have operator for merging.
Isn't "for consistency with other types" a wrong consistency?
> but requires either some obscure syntax or a statement instead of a simple
> expression.
>
> The proposal is to enable the obvious syntax for something that should be
> obvious.
dict.update is obvious already. Why statement is not enough?
Regards,
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