Message374516
The following code raises a ZeroDivisionError:
from random import Random
Random(14064741636871487939).paretovariate(0.01)
This raises:
random.py, line 692, in paretovariate
return 1.0 / u ** (1.0/alpha)
ZeroDivisionError: float division by zero
That specific stack trace is from 3.8.5 but I've tried this on 3.6 and 3.7 as well.
It's a little hard to tell what the intended correct range of parameter values is for paretovariate, and this may just be lack of validation for the alpha < 1 case - perhaps that was never intended to be supported?
Based on some very informal inspection, what seems to happen is that the probability of getting a ZeroDivisionError approaches one as you approach zero. They rarely occur at this level of alpha (0.01), but for alpha=0.001 they seem to occur just under half the time, and for alpha=0.0001 they occur more than 90% of the time.
(For the interested, this bug was found by Hypothesis as part of its own testing of our integration with the Random API) |
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Date |
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2020-07-28 17:59:09 | David MacIver | set | recipients:
+ David MacIver |
2020-07-28 17:59:09 | David MacIver | set | messageid: <1595959149.08.0.339696183777.issue41421@roundup.psfhosted.org> |
2020-07-28 17:59:09 | David MacIver | link | issue41421 messages |
2020-07-28 17:59:08 | David MacIver | create | |
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