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Author mark.dickinson
Recipients Kostis Gourgoulias, mark.dickinson, ned.deily, ronaldoussoren
Date 2020-02-20.17:07:59
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Message-id <1582218479.3.0.648816560311.issue39703@roundup.psfhosted.org>
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> Shouldn't the two approaches provide the same answer?

In a word, no. :-)

math.floor(1/0.01) involves *two* operations, and there's an intermediate rounding step which happens to round the true mathematical result of 1/0.01 up to 100.0. Taking the floor of that then (of course) gives 100.0.

1//0.01 is the single-operation equivalent, that doesn't include an intermediate round.

There are lots of other cases where a combination of two or more operations is mathematically equivalent to a single operation, but produces a different result due to an intermediate round; for example, things like `log(n) / log(2)` versus `log2(n)`, or `round(x, 2)` versus `round(100.0*x)/100.0`.

There's unfortunately no way to square the circle here that doesn't cause surprises in at least some corner cases.

I'm almost sure this issue is a duplicate, but I haven't found a good target for that duplicate yet. I'll continue searching.
History
Date User Action Args
2020-02-20 17:07:59mark.dickinsonsetrecipients: + mark.dickinson, ronaldoussoren, ned.deily, Kostis Gourgoulias
2020-02-20 17:07:59mark.dickinsonsetmessageid: <1582218479.3.0.648816560311.issue39703@roundup.psfhosted.org>
2020-02-20 17:07:59mark.dickinsonlinkissue39703 messages
2020-02-20 17:07:59mark.dickinsoncreate