17.06.21 06:03, David Mertz пише:
> I'm sympathetic to raising an exception on `sum(list_of_lists)` similar
> to `sum(list_of_strings)`. But what exactly is the recommended
> substitute? We have this:
>
> list(chain.from_iterable(list_of_lists))
>
> Which is pretty nice, and what I'd probably do, but it DOES require
> importing from itertools to use it. That feels like a drawback, at
> least a minor one.
And it is equivalent to pure Python code
[x for chunk in list_of_lists for x in chunk]
It has linear complexity and is only by a constant factor slower because
it iterates loops in bytecode instead of the C code. It would be
possible to make the compiler recognizing such pattern and generating
more efficient bytecode (LIST_EXTEND instead of an internal loop with
LIST_APPEND), but I am not sure that this case is common enough to
complicate the compiler.
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