28.02.19 23:19, Greg Ewing пише:
Serhiy Storchaka wrote:
I do not understand why we discuss a new syntax for dict merging if we
already have a syntax for dict merging: {**d1, **d2} (which works with
*all* mappings).
But that always returns a dict. A '+' operator could be implemented
by other mapping types to return a mapping of the same type.
And this opens a non-easy problem: how to create a mapping of the same
type? Not all mappings, and even not all dict subclasses have a copying
constructor.
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