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Issue #18844: Make the number of selections a keyword-only argument for random.choices().

This commit is contained in:
Raymond Hettinger 2016-09-26 21:45:57 -07:00
parent 22805ca54e
commit 9016f2864a
4 changed files with 27 additions and 23 deletions
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2
Doc/library/random.rst
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@ -124,7 +124,7 @@ Functions for sequences:
Return a random element from the non-empty sequence *seq*. If *seq* is empty,
raises :exc:`IndexError`.
.. function:: choices(k, population, weights=None, *, cum_weights=None)
.. function:: choices(population, weights=None, *, cum_weights=None, k=1)
Return a *k* sized list of elements chosen from the *population* with replacement.
If the *population* is empty, raises :exc:`IndexError`.

2
Lib/random.py
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@ -337,7 +337,7 @@ class Random(_random.Random):
result[i] = population[j]
return result
def choices(self, k, population, weights=None, *, cum_weights=None):
def choices(self, population, weights=None, *, cum_weights=None, k=1):
"""Return a k sized list of population elements chosen with replacement.
If the relative weights or cumulative weights are not specified,

42
Lib/test/test_random.py
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@ -151,8 +151,8 @@ class TestBasicOps:
# basic functionality
for sample in [
choices(5, data),
choices(5, data, range(4)),
choices(data, k=5),
choices(data, range(4), k=5),
choices(k=5, population=data, weights=range(4)),
choices(k=5, population=data, cum_weights=range(4)),
]:
@ -164,50 +164,50 @@ class TestBasicOps:
with self.assertRaises(TypeError): # missing arguments
choices(2)
self.assertEqual(choices(0, data), []) # k == 0
self.assertEqual(choices(-1, data), []) # negative k behaves like ``[0] * -1``
self.assertEqual(choices(data, k=0), []) # k == 0
self.assertEqual(choices(data, k=-1), []) # negative k behaves like ``[0] * -1``
with self.assertRaises(TypeError):
choices(2.5, data) # k is a float
choices(data, k=2.5) # k is a float
self.assertTrue(set(choices(5, str_data)) <= set(str_data)) # population is a string sequence
self.assertTrue(set(choices(5, range_data)) <= set(range_data)) # population is a range
self.assertTrue(set(choices(str_data, k=5)) <= set(str_data)) # population is a string sequence
self.assertTrue(set(choices(range_data, k=5)) <= set(range_data)) # population is a range
with self.assertRaises(TypeError):
choices(2.5, set_data) # population is not a sequence
choices(set_data, k=2) # population is not a sequence
self.assertTrue(set(choices(5, data, None)) <= set(data)) # weights is None
self.assertTrue(set(choices(5, data, weights=None)) <= set(data))
self.assertTrue(set(choices(data, None, k=5)) <= set(data)) # weights is None
self.assertTrue(set(choices(data, weights=None, k=5)) <= set(data))
with self.assertRaises(ValueError):
choices(5, data, [1,2]) # len(weights) != len(population)
choices(data, [1,2], k=5) # len(weights) != len(population)
with self.assertRaises(IndexError):
choices(5, data, [0]*4) # weights sum to zero
choices(data, [0]*4, k=5) # weights sum to zero
with self.assertRaises(TypeError):
choices(5, data, 10) # non-iterable weights
choices(data, 10, k=5) # non-iterable weights
with self.assertRaises(TypeError):
choices(5, data, [None]*4) # non-numeric weights
choices(data, [None]*4, k=5) # non-numeric weights
for weights in [
[15, 10, 25, 30], # integer weights
[15.1, 10.2, 25.2, 30.3], # float weights
[Fraction(1, 3), Fraction(2, 6), Fraction(3, 6), Fraction(4, 6)], # fractional weights
[True, False, True, False] # booleans (include / exclude)
]:
self.assertTrue(set(choices(5, data, weights)) <= set(data))
self.assertTrue(set(choices(data, weights, k=5)) <= set(data))
with self.assertRaises(ValueError):
choices(5, data, cum_weights=[1,2]) # len(weights) != len(population)
choices(data, cum_weights=[1,2], k=5) # len(weights) != len(population)
with self.assertRaises(IndexError):
choices(5, data, cum_weights=[0]*4) # cum_weights sum to zero
choices(data, cum_weights=[0]*4, k=5) # cum_weights sum to zero
with self.assertRaises(TypeError):
choices(5, data, cum_weights=10) # non-iterable cum_weights
choices(data, cum_weights=10, k=5) # non-iterable cum_weights
with self.assertRaises(TypeError):
choices(5, data, cum_weights=[None]*4) # non-numeric cum_weights
choices(data, cum_weights=[None]*4, k=5) # non-numeric cum_weights
with self.assertRaises(TypeError):
choices(5, data, range(4), cum_weights=range(4)) # both weights and cum_weights
choices(data, range(4), cum_weights=range(4), k=5) # both weights and cum_weights
for weights in [
[15, 10, 25, 30], # integer cum_weights
[15.1, 10.2, 25.2, 30.3], # float cum_weights
[Fraction(1, 3), Fraction(2, 6), Fraction(3, 6), Fraction(4, 6)], # fractional cum_weights
]:
self.assertTrue(set(choices(5, data, cum_weights=weights)) <= set(data))
self.assertTrue(set(choices(data, cum_weights=weights, k=5)) <= set(data))
def test_gauss(self):
# Ensure that the seed() method initializes all the hidden state. In

4
Misc/NEWS
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@ -44,6 +44,10 @@ Library
- Issue #27897: Fixed possible crash in sqlite3.Connection.create_collation()
if pass invalid string-like object as a name. Patch by Xiang Zhang.
- Issue #18844: random.choices() now has k as a keyword-only argument
to improve the readability of common cases and the come into line
with the signature used in other languages.
- Issue #18893: Fix invalid exception handling in Lib/ctypes/macholib/dyld.py.
Patch by Madison May.