Hi! On 2017-09-16, Nils Bruin <nbr...@sfu.ca> wrote: > 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).
Here are some timings: sage: def test_local(): ....: import gc ....: return gc.isenabled() ....: sage: def test_conditional(): ....: global gc ....: try: ....: return gc.isenabled() ....: except NameError: ....: import gc ....: return gc.isenabled() ....: sage: %timeit test_conditional() The slowest run took 17.65 times longer than the fastest. This could mean that an intermediate result is being cached. 10000000 loops, best of 3: 122 ns per loop sage: %timeit test_local() The slowest run took 19.69 times longer than the fastest. This could mean that an intermediate result is being cached. 1000000 loops, best of 3: 555 ns per loop Thus, if an import on module level were circular, one can break the circle by making a *conditional* *global* import *locally*. And it is substantially faster than an unconditional local import. The following variation of the conditional import is taken from https://wiki.python.org/moin/PythonSpeed/PerformanceTips and is slightly easier to read, but also slightly slower than test_conditional above: sage: gc = None sage: def test_conditional2(): ....: global gc ....: if gc is None: ....: import gc ....: return gc.isenabled() ....: sage: %timeit test_conditional2() The slowest run took 60.73 times longer than the fastest. This could mean that an intermediate result is being cached. 10000000 loops, best of 3: 133 ns per loop Best regards, Simon -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
