On Friday, September 15, 2017 at 2:28:06 PM UTC-7, Travis Scrimshaw wrote:
>
>
> Why are you proposing local imports? If python puts a performance penalty
>> on them (in fact a significant performance penalty), they should be
>> avoided, no?
>>
>> It is a relatively small penalty, so when it is not in a tight loop, it
> is useful to break out of those cyclic imports (and has better locality of
> reference).
>
For the most part, Python should be able to handle circular imports on the
top-level. The obvious problems arise if we have
A:
from B import b
B:
from A import a
Normally, what should be OK is
A:
import B
def ...:
B.b(bla)
B:
import A
def ...:
A.a(bla)
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. If
that's a bunch of levels deep, you could try "import ..... as ..." at
toplevel instead, so that there's a direct pointer to the relevant
namespace (in case the multiple indirections still cause too much overhead).
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