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Misc cleanups and wording improvements for the itertools docs #119626

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Merged
rhettinger merged 16 commits into from
May 27, 2024
+116 −122
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Misc cleanups and wording improvements for the itertools docs #119626

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e42bf24
Tighten the wording for permutations(). Add links.
rhettinger May 25, 2024
2c2bb68
Tighten the wording for combinations(). Add links.
rhettinger May 25, 2024
269b506
Tighten the wording for combinations_with_replacement().
rhettinger May 25, 2024
642e89f
Tighen wording for islice()
rhettinger May 25, 2024
c581a38
Swap sentence order
rhettinger May 26, 2024
598c414
.
rhettinger May 26, 2024
a558705
Sync table examples with main docs
rhettinger May 27, 2024
2974acd
Improve readability of the amortization example
rhettinger May 27, 2024
295baa4
Improve accumulate() docs
rhettinger May 27, 2024
d3e6800
.
rhettinger May 27, 2024
1f52c89
Improve wording for compress()
rhettinger May 27, 2024
95f503b
Improve wording for count()
rhettinger May 27, 2024
61f629d
Tighter wording for cycle()
rhettinger May 27, 2024
95e82ed
Improve wording for dropwhile()
rhettinger May 27, 2024
6cfce87
Misc wording tweaks
rhettinger May 27, 2024
d60c375
Tweak starmap() wording
rhettinger May 27, 2024
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Tighten the wording for permutations(). Add links.
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@rhettinger
rhettinger committed May 25, 2024
commit e42bf24990b4ee032fd4703f0d66d1c1f0c57111
26 changes: 9 additions & 17 deletions Doc/library/itertools.rst
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Expand Up @@ -534,18 +534,24 @@ loops that truncate the stream.

.. function:: permutations(iterable, r=None)

Return successive *r* length permutations of elements in the *iterable*.
Return successive *r* length `permutations of elements
<https://www.britannica.com/science/permutation>`_ from the *iterable*.

If *r* is not specified or is ``None``, then *r* defaults to the length
of the *iterable* and all possible full-length permutations
are generated.

The output is a subsequence of :func:`product` where entries with
repeated elements have been filtered out. The length of the output is
given by :func:`math.perm` which gives ``n! / (n-r)!`` when ``0 <= r <=
n`` or zero when ``r > n``.

The permutation tuples are emitted in lexicographic order according to
the order of the input *iterable*. So, if the input *iterable* is sorted,
the order of the input *iterable*. If the input *iterable* is sorted,
the output tuples will be produced in sorted order.

Elements are treated as unique based on their position, not on their
value. So, if the input elements are unique, there will be no repeated
value. If the input elements are unique, there will be no repeated
values within a permutation.

Roughly equivalent to::
Expand Down Expand Up @@ -578,20 +584,6 @@ loops that truncate the stream.
else:
return

The code for :func:`permutations` can be also expressed as a subsequence of
:func:`product` filtered to exclude entries with repeated elements (those
from the same position in the input pool)::

def permutations(iterable, r=None):
pool = tuple(iterable)
n = len(pool)
r = n if r is None else r
for indices in product(range(n), repeat=r):
if len(set(indices)) == r:
yield tuple(pool[i] for i in indices)

The number of items returned is ``n! / (n-r)!`` when ``0 <= r <= n``
or zero when ``r > n``.

.. function:: product(*iterables, repeat=1)

Expand Down