Set union (| operator) is commutative.
>>> {2,3} | {1,2} == {1,2} | {2,3}
True
List concatenation isn't
>>> [2,3] + [1,2] == [1,2] + [2,3]
False
so maybe the expectation of commutativity for + isn't a good argument (or is an
argument that list concatenation should be called something else :) ).
If you want a (verbose) one-liner for "concatenation" of dictionaries, there's
always:
dict(itertools.chain({1:1}.iteritems(), {2:2}.iteritems()))
On 17/10/2013, at 11:31 AM, Sam Lai <[email protected]> wrote:
> It's almost Friday, so I have a question where I'm pretty sure I'm
> missing something obvious.
>
> Given,
>
> d1 = { 'a' : 'b' }
> d2 = { 'c' : 'd' }
>
> ... why isn't d3 = d1 + d2 implemented to be equivalent to -
>
> d3 = { }
> d3.update(d1)
> d3.update(d2)
>
> It doesn't work for sets either, but it works in this fashion for
> lists. Is this because the operation is non-commutative for sets and
> dicts and may result in a loss of data when clashing keys are
> involved? Isn't that implicit when working with sets and dicts?
>
> Sam
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> melbourne-pug mailing list
> [email protected]
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