Mark Dickinson added the comment:
A similar bug affects the new `choices` method: in the `choices` source, if
`random() * total` happens to round up to `total`, the bisect call returns an
out-of-range index.
There are two ways that that could happen: (1) double rounding, as in this
issue (which will occur very rarely and is hard to reproduce), and (2) `total`
being subnormal (easy to reproduce, but unlikely to occur in practice).
>>> from random import choices
>>> choices(500, population=[1, 2], weights=[1e-323, 1e-323])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/mdickinson/Python/cpython/Lib/random.py", line 360, in choices
return [population[bisect(cum_weights, random() * total)] for i in range(k)]
File "/Users/mdickinson/Python/cpython/Lib/random.py", line 360, in <listcomp>
return [population[bisect(cum_weights, random() * total)] for i in range(k)]
IndexError: list index out of range
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<http://bugs.python.org/issue24567>
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