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[3.12] Remove itertool recipe with low pedagogical value (gh-113138) (gh-113140)

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Miss Islington (bot) 2023-12-14 21:42:36 +01:00 • committed by GitHub
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64
Doc/library/itertools.rst
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@ -1135,24 +1135,6 @@ The following recipes have a more mathematical flavor:
n = n // p * (p - 1) n = n // p * (p - 1)
return n return n
def nth_combination(iterable, r, index):
"Equivalent to list(combinations(iterable, r))[index]"
pool = tuple(iterable)
n = len(pool)
c = math.comb(n, r)
if index < 0:
index += c
if index < 0 or index >= c:
raise IndexError
result = []
while r:
c, n, r = c*r//n, n-1, r-1
while index >= c:
index -= c
c, n = c*(n-r)//n, n-1
result.append(pool[-1-n])
return tuple(result)
.. doctest:: .. doctest::
:hide: :hide:
@ -1576,20 +1558,6 @@ The following recipes have a more mathematical flavor:
>>> first_true('ABC0DEF1', '9', str.isdigit) >>> first_true('ABC0DEF1', '9', str.isdigit)
'0' '0'
>>> population = 'ABCDEFGH'
>>> for r in range(len(population) + 1):
... seq = list(combinations(population, r))
... for i in range(len(seq)):
... assert nth_combination(population, r, i) == seq[i]
... for i in range(-len(seq), 0):
... assert nth_combination(population, r, i) == seq[i]
>>> iterable = 'abcde'
>>> r = 3
>>> combos = list(combinations(iterable, r))
>>> all(nth_combination(iterable, r, i) == comb for i, comb in enumerate(combos))
True
.. testcode:: .. testcode::
:hide: :hide:
@ -1616,6 +1584,24 @@ The following recipes have a more mathematical flavor:
for (a, _), (b, c) in pairwise(pairwise(iterable)): for (a, _), (b, c) in pairwise(pairwise(iterable)):
yield a, b, c yield a, b, c
def nth_combination(iterable, r, index):
"Equivalent to list(combinations(iterable, r))[index]"
pool = tuple(iterable)
n = len(pool)
c = math.comb(n, r)
if index < 0:
index += c
if index < 0 or index >= c:
raise IndexError
result = []
while r:
c, n, r = c*r//n, n-1, r-1
while index >= c:
index -= c
c, n = c*(n-r)//n, n-1
result.append(pool[-1-n])
return tuple(result)
.. doctest:: .. doctest::
:hide: :hide:
@ -1631,3 +1617,17 @@ The following recipes have a more mathematical flavor:
>>> list(triplewise('ABCDEFG')) >>> list(triplewise('ABCDEFG'))
[('A', 'B', 'C'), ('B', 'C', 'D'), ('C', 'D', 'E'), ('D', 'E', 'F'), ('E', 'F', 'G')] [('A', 'B', 'C'), ('B', 'C', 'D'), ('C', 'D', 'E'), ('D', 'E', 'F'), ('E', 'F', 'G')]
>>> population = 'ABCDEFGH'
>>> for r in range(len(population) + 1):
... seq = list(combinations(population, r))
... for i in range(len(seq)):
... assert nth_combination(population, r, i) == seq[i]
... for i in range(-len(seq), 0):
... assert nth_combination(population, r, i) == seq[i]
>>> iterable = 'abcde'
>>> r = 3
>>> combos = list(combinations(iterable, r))
>>> all(nth_combination(iterable, r, i) == comb for i, comb in enumerate(combos))
True