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bpo-35723: Proof of concept for tzidx cache #11529
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pganssle
changed the title
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Hm, in an earlier version of this I got a segfault when I had some accidental recursion in the I suppose for now I'll assume the segfault was for some other reason and that it is fixed now, but if anyone can come up with an example of a tzinfo implemented with recursion that causes a segfault, I'll add and fix it. |
As with the other tzinfo methods, datetime.tzidx is now implemented in terms of tzinfo.tzidx, with some additional strictness because of the nature of the tzidx method.
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This PR is stale because it has been open for 30 days with no activity. |
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I believe this is no longer necessary. |
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When examining the performance characteristics of pytz, I realized that pytz's eager calculation of tzname, offset and DST gives it an implicit cache that makes it much faster for repeated queries to .utcoffset(), .dst() and/or .tzname(), see my blog post "pytz: The Fastest Footgun in the West", though the eager calculation means that it's slower to create an aware datetime that never calculates those functions.
This proof of concept introduces a "set once" cache to the
datetimeobject thattzinfoimplementations can use to cache offset and name lookups per datetime. A more thorough discussion of the rationale for this change is available on the associated issue, bpo-35723.I will note that this is currently a WIP, it still needs:
tzidxis not an integer, or outside the interval [0, 254]https://bugs.python.org/issue35723