Georg Brandl wrote:
>In the meantime, I played around with the peepholer and tried to copy
>the "for x in tuple_or_list" optimization for sets. Results are in SF
>patch #1548082.
>
>
>
Did you mean "if x in tuple_or_list"? IIRC, there was some reason that
mutable lists were not supposed to be made into constants in for-loops.
>* list comprehensions are special-cased because of the LIST_APPEND opcode.
> If there isn't going to be a special-cased SET_ADD, it's probably the
> easiest thing to transform {x for x in a} into set(x for x in a) in the
> AST step, with "set" of course always being the builtin set.
>
>
>
Set comprehensions and list comprehensions are fundamentally the same
and therefore should have identical implementations.
While transformation to a generator expression may seem like a good idea
now, I expect that you'll observe a two-fold performance hit and end-up
abandoning that approach in favor of the current LIST_APPEND approach.
So it would probably be best to start by teaching the compiler to hide
the loop variable in a LIST_APPEND approach to list comprehensions and
then duplicate that approach for set comprehensions.
Raymond
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