Author Alex.Willmer
Recipients Alex.Willmer, docs@python
Date 2021-03-04.22:34:08
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Discussion from #python IRC

[21:51] <moreati> Given `a=time.monotonic(); b=time.monotonic(); c=time.monotonic()` is `c-a < delta` a valid comparison? Until this evening I thought so, but I've just read https://docs.python.org/3/library/time.html#time.monotonic and the wording it uses is "only the difference between the results of consecutive calls is valid" implying `b-a < delta` is valid, or `c-b < delta`; but not `c-a < delta`. Am I understanding the wording correctly?
[21:52] <moreati> IOW is it literally only call n, and n+1. or n, and n+m?
[21:53] <SnoopJ> moreati, I think "consecutive" is incorrect there, based on the rest of that sentence.
[21:57] <jarthur> moreati SnoopJ yes, I agree, the consecutive wording has tripped me up when I first started using monotonic. I think there's an understated transitive property that allows a to c comparisons just fine.
[21:58] <SnoopJ> jarthur, yea, it would be deeply weird if `b-a` and `c-b` were meaningful deltas, but `c-a` was not
[21:59] <moreati> re time.monotonic() the only reason I could of for the literal interpretation of the wording is an overflow, or integer wraparound corner case
[22:00] <SnoopJ> weirdly, the CPython doc uses the same language
[22:02] <jarthur> I actually ended up looking at the monotonic code a while back, and at least back then the wraparound case is really hard to reach, maybe possible on Windows if you haven't called it in a while. Either way, there was nothing in the Linux/glibc or Windows calls used that would have made the wraparound/overflow case apply to skipped evaluation of a middle observation more than it would consecutive observations.
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[22:06] <SnoopJ> moreati, looks like this language was added when the function was, and I guess maybe nobody's ever raised this complaint about the wording: https://hg.python.org/cpython/rev/376ce937823c
[22:07] <SnoopJ> nice catch :)
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[22:22] <moreati> FTR https://bugs.python.org/issue43407
[22:28] <SnoopJ> moreati, I would recommend just submitting the PR, since it's docs.
[22:28] <moreati> ok
[22:28] <SnoopJ> but I think the best wording would be something like "only the difference between two calls of this function is meaningful"
[22:30] <moreati> agreed, subsequent is a $5 word in a 50c requirement. May I quote our conversation in the ticket? Ditto jarthur
[22:30] <SnoopJ> absolutely
[22:30] <jarthur> yep
[22:30] <moreati> ty
[22:30] <SnoopJ> but yea, just open a PR, that way you need a single pass from someone with authority here rather than two ;)
[22:31] <grym> >Never use a long word where a short one will do.
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2021-03-04 22:34:08Alex.Willmersetrecipients: + Alex.Willmer, docs@python
2021-03-04 22:34:08Alex.Willmersetmessageid: <1614897248.6.0.983455919755.issue43407@roundup.psfhosted.org>
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