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One argument form of math.perm() #81359

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rhettinger opened this issue Jun 6, 2019 · 7 comments
Closed

One argument form of math.perm() #81359

rhettinger opened this issue Jun 6, 2019 · 7 comments
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3.8 only security fixes 3.9 only security fixes stdlib Python modules in the Lib dir

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@rhettinger
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BPO 37178
Nosy @tim-one, @rhettinger, @mdickinson, @serhiy-storchaka
PRs
  • bpo-37178: Allow a one argument form of math.perm() #13905
  • [3.8] bpo-37178: Allow a one argument form of math.perm() (GH-13905) #13919
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = <Date 2019-06-08.23:55:34.895>
created_at = <Date 2019-06-06.16:30:28.309>
labels = ['3.8', 'library', '3.9']
title = 'One argument form of math.perm()'
updated_at = <Date 2019-06-08.23:55:34.895>
user = 'https://github.com/rhettinger'

    bugs.python.org fields:

    activity = <Date 2019-06-08.23:55:34.895>
actor = 'rhettinger'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-08.23:55:34.895>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2019-06-06.16:30:28.309>
creator = 'rhettinger'
dependencies = []
files = []
hgrepos = []
issue_num = 37178
keywords = ['patch']
message_count = 7.0
messages = ['344833', '344835', '344837', '344840', '345020', '345053', '345054']
nosy_count = 4.0
nosy_names = ['tim.peters', 'rhettinger', 'mark.dickinson', 'serhiy.storchaka']
pr_nums = ['13905', '13919']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue37178'
versions = ['Python 3.8', 'Python 3.9']
    @rhettinger
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    The perm() function should have a one argument form and change its signature to perm(n, k=None). This matches what itertools:

    itertools.permutations(iterable, r=None)
   Return successive r length permutations of elements
   in 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.

    @rhettinger rhettinger added 3.8 only security fixes 3.9 only security fixes stdlib Python modules in the Lib dir labels Jun 6, 2019
    @serhiy-storchaka
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    perm(n, n) = factorial(n)

    @tim-one
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    tim-one commented Jun 6, 2019

    I agree: perm(n) should return factorial(n).

    @serhiy-storchaka
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    I never seen a one argument form of P(n, k) in mathematics. itertools.permutations() corresponds two functions: math.perm() and math .factorial(). Unless you a going to add a new function in the itertools module equal to a one argument form of itertools.permutations() there will be no full symmetry.

    @rhettinger
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    It's possible the word permutations means something different to you than it does to me. The itertools.permutations() function is only one function, one that includes the default option to generate all permutations. It does the same as permute(n, r) and permute(n) in Maple; and the same as Permutations[list, n] and Permutations[list] in Mathematica. For the math module, perm(n) is just a common special case that means all possible arrangements.

    @rhettinger
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    New changeset e119b3d by Raymond Hettinger in branch 'master':
    bpo-37178: Allow a one argument form of math.perm() (GH-13905)
    e119b3d

    @rhettinger
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    New changeset feaceaa by Raymond Hettinger (Miss Islington (bot)) in branch '3.8':
    bpo-37178: Allow a one argument form of math.perm() (GH-13905) (GH-13919)
    feaceaa

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
    @skirpichev skirpichev mentioned this issue Feb 10, 2023
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