https://github.com/python/cpython/commit/b0dfc7581697f20385813582de7e92ba6ba... commit: b0dfc7581697f20385813582de7e92ba6ba0105f branch: master author: Ram Rachum <ram@rachum.com> committer: GitHub <noreply@github.com> date: 2020-09-28T18:32:10-07:00 summary: bpo-41773: Raise exception for non-finite weights in random.choices(). (GH-22441) files: A Misc/NEWS.d/next/Library/2020-09-28-23-22-25.bpo-41773.oKkus0.rst M Doc/library/random.rst M Lib/random.py M Lib/test/test_random.py diff --git a/Doc/library/random.rst b/Doc/library/random.rst index 0cdf0a6ac4a47..af5131df280c2 100644 --- a/Doc/library/random.rst +++ b/Doc/library/random.rst @@ -180,8 +180,8 @@ Functions for sequences The *weights* or *cum_weights* can use any numeric type that interoperates with the :class:`float` values returned by :func:`random` (that includes - integers, floats, and fractions but excludes decimals). Behavior is - undefined if any weight is negative. A :exc:`ValueError` is raised if all + integers, floats, and fractions but excludes decimals). Weights are assumed + to be non-negative and finite. A :exc:`ValueError` is raised if all weights are zero. For a given seed, the :func:`choices` function with equal weighting diff --git a/Lib/random.py b/Lib/random.py index 3ea369b81b3e5..139e8a40bb272 100644 --- a/Lib/random.py +++ b/Lib/random.py @@ -48,7 +48,7 @@ from warnings import warn as _warn from math import log as _log, exp as _exp, pi as _pi, e as _e, ceil as _ceil from math import sqrt as _sqrt, acos as _acos, cos as _cos, sin as _sin -from math import tau as TWOPI, floor as _floor +from math import tau as TWOPI, floor as _floor, isfinite as _isfinite from os import urandom as _urandom from _collections_abc import Set as _Set, Sequence as _Sequence from itertools import accumulate as _accumulate, repeat as _repeat @@ -492,6 +492,8 @@ def choices(self, population, weights=None, *, cum_weights=None, k=1): total = cum_weights[-1] + 0.0 # convert to float if total <= 0.0: raise ValueError('Total of weights must be greater than zero') + if not _isfinite(total): + raise ValueError('Total of weights must be finite') bisect = _bisect hi = n - 1 return [population[bisect(cum_weights, random() * total, 0, hi)] diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py index a80e71e67e4c6..0c1fdeec9915e 100644 --- a/Lib/test/test_random.py +++ b/Lib/test/test_random.py @@ -324,6 +324,22 @@ def test_choices_with_all_zero_weights(self): with self.assertRaises(ValueError): self.gen.choices('AB', [0.0, 0.0]) + def test_choices_negative_total(self): + with self.assertRaises(ValueError): + self.gen.choices('ABC', [3, -5, 1]) + + def test_choices_infinite_total(self): + with self.assertRaises(ValueError): + self.gen.choices('A', [float('inf')]) + with self.assertRaises(ValueError): + self.gen.choices('AB', [0.0, float('inf')]) + with self.assertRaises(ValueError): + self.gen.choices('AB', [-float('inf'), 123]) + with self.assertRaises(ValueError): + self.gen.choices('AB', [0.0, float('nan')]) + with self.assertRaises(ValueError): + self.gen.choices('AB', [float('-inf'), float('inf')]) + def test_gauss(self): # Ensure that the seed() method initializes all the hidden state. In # particular, through 2.2.1 it failed to reset a piece of state used diff --git a/Misc/NEWS.d/next/Library/2020-09-28-23-22-25.bpo-41773.oKkus0.rst b/Misc/NEWS.d/next/Library/2020-09-28-23-22-25.bpo-41773.oKkus0.rst new file mode 100644 index 0000000000000..cef7ff0188354 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2020-09-28-23-22-25.bpo-41773.oKkus0.rst @@ -0,0 +1,2 @@ +Note in documentation that :func:`random.choices` doesn't support non-finite +weights, raise :exc:`ValueError` when given non-finite weights.