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gh-96545 make random.sample'k argument optional #96546

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455bccc
Make random.sample's k argument optional
Gouvernathor Sep 3, 2022
0e647a5
Document changes to random.sample
Gouvernathor Sep 3, 2022
96f3e9e
Remove trailing whitespace
Gouvernathor Sep 3, 2022
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8 changes: 7 additions & 1 deletion Doc/library/random.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -224,7 +224,7 @@ Functions for sequences
The optional parameter *random*.


.. function:: sample(population, k, *, counts=None)
.. function:: sample(population, k=None, *, counts=None)

Return a *k* length list of unique elements chosen from the population
sequence. Used for random sampling without replacement.
Expand All @@ -238,6 +238,10 @@ Functions for sequences
Members of the population need not be :term:`hashable` or unique. If the population
contains repeats, then each occurrence is a possible selection in the sample.

The number of elements to sample is specified through the *k* parameter. If
omitted, it defaults to ``len(population)``, and the function returns a shuffled
copy of the sequence.

Repeated elements can be specified one at a time or with the optional
keyword-only *counts* parameter. For example, ``sample(['red', 'blue'],
counts=[4, 2], k=5)`` is equivalent to ``sample(['red', 'red', 'red', 'red',
Expand All @@ -258,6 +262,8 @@ Functions for sequences
The *population* must be a sequence. Automatic conversion of sets
to lists is no longer supported.

The *k* argument is now optional.

Discrete distributions
----------------------

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4 changes: 3 additions & 1 deletion Lib/random.py
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Expand Up @@ -349,7 +349,7 @@ def shuffle(self, x):
j = randbelow(i + 1)
x[i], x[j] = x[j], x[i]

def sample(self, population, k, *, counts=None):
def sample(self, population, k=None, *, counts=None):
"""Chooses k unique random elements from a population sequence.

Returns a new list containing elements from the population while
Expand Down Expand Up @@ -406,6 +406,8 @@ def sample(self, population, k, *, counts=None):
raise TypeError("Population must be a sequence. "
"For dicts or sets, use sorted(d).")
n = len(population)
if k is None:
k = n
if counts is not None:
cum_counts = list(_accumulate(counts))
if len(cum_counts) != n:
Expand Down