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fix: Potentially undefined behaviour when initialised with invalid probability distribution. #16

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fix: Potentially undefined behaviour when initialised with invalid probability distribution. #16

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2 changes: 2 additions & 0 deletions vose_sampler/vose_sampler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,8 @@ class VoseAlias(object):

def __init__(self, dist, rng=None):
""" (VoseAlias, dict[, RNG]) -> NoneType """
if sum(dist.values()) != 1:

@austin-bowen austin-bowen Aug 12, 2026

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I recommend checking if the sum is close to 1 instead of exactly 1, since we are summing floats, which is unlikely except in simple cases to actually add to exactly 1. See math.isclose(): https://docs.python.org/3/library/math.html#math.isclose

@asmith26 asmith26 Aug 14, 2026

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Thanks for the review @austin-bowen, this sounds good to me!

Thanks very much also @webbrain-one for this addition! Should be good to merge once this is added - I've also just added automated checks/GitHub Actions in #17, so you may need to merge main to pick these up.

Thanks again!

raise ValueError("Probability distribution must sum to 1.")
self.dist = dist
self.rng = rng or random.Random()
self.alias_initialisation()
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