On Monday, September 18, 2017 at 3:08:11 AM UTC-7, Jeroen Demeyer wrote:
>
> On 2017-09-16 03:31, Nils Bruin wrote:
> > So if you're finding you can't put a "from A import a" at the top-level
> > and using it locally has noticeable cost (which can easily happen:
> > imports have a significant cost, even for modules that are already
> > present), then you could try to do a straight import and access the
> > appropriate namespace.
>
> But accessing the namespace is also slower than doing the "from ...
> import ..." import:
>
> sage: x = 42
> sage: timeit("sage.structure.element.parent(x)", number=20, repeat=10^6)
> 20 loops, best of 1000000: 143 ns per loop
> sage: timeit("parent(x)", number=20, repeat=10^6)
> 20 loops, best of 1000000: 47.7 ns per loop
>
> Yes, that is where the name-space-tree-flattening tool
sage: import sage.structure.element as elm
comes in handy. With that I get:
sage: timeit("sage.structure.element.parent(x)", number=20, repeat=10^6)
20 loops, best of 1000000: 143 ns per loop
sage: timeit("elm.parent(x)", number=20, repeat=10^6)
20 loops, best of 1000000: 47.7 ns per loop
sage: timeit("parent(x)", number=20, repeat=10^6)
20 loops, best of 1000000: 47.7 ns per loop
I'm very surprised we're getting exactly the same timings. I'm also a
little suspicious there's no difference measured between the 2nd and 3rd
test. I think it indicates it helps quite a bit.
Of course, if you *really* care about this overhead, you should make sure
that a significant part of the loop lies in one function and that the
function lookup is from a local variable (not a global). I'm hopeful that
the above indicates that in most cases we can get acceptable performance
with a renamed global import of the module, without having to rebind
particular objects from it to global/local variables in a different module
via a "from ... import ..." construction, and that in many cases this is
enough to avoid the circular import problems we encounter otherwise.
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