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Add math.perm() #81309

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serhiy-storchaka opened this issue Jun 1, 2019 · 4 comments
Closed

Add math.perm() #81309

serhiy-storchaka opened this issue Jun 1, 2019 · 4 comments
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3.8 only security fixes stdlib Python modules in the Lib dir type-feature A feature request or enhancement

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@serhiy-storchaka
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BPO 37128
Nosy @malemburg, @rhettinger, @mdickinson, @serhiy-storchaka
PRs
  • bpo-37128: Add math.perm(). #13731
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    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 2019-06-02.08:53:34.710>
created_at = <Date 2019-06-01.20:47:29.810>
labels = ['3.8', 'type-feature', 'library']
title = 'Add math.perm()'
updated_at = <Date 2019-06-02.08:53:41.312>
user = 'https://github.com/serhiy-storchaka'

    bugs.python.org fields:

    activity = <Date 2019-06-02.08:53:41.312>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-02.08:53:34.710>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2019-06-01.20:47:29.810>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 37128
keywords = ['patch']
message_count = 4.0
messages = ['344226', '344227', '344228', '344259']
nosy_count = 5.0
nosy_names = ['lemburg', 'rhettinger', 'mark.dickinson', 'stutzbach', 'serhiy.storchaka']
pr_nums = ['13731']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue37128'
versions = ['Python 3.8']
    @serhiy-storchaka
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    The function which returns the number of ways to choose k items from n items without repetition and without order was added in bpo-35431. This functions is always goes in pair with other function, which returns the number of ways to choose k items from n items without repetition and with order. These functions are always learned together in curses of combinatorics. Often C(n,k) is determined via P(n,k) (and both are determined via factorial).

    P(n, k) = n! / (n-k)!
C(n, k) = P(n, k) / k!

    The proposed PR adds meth.perm(). It shares most of the code with math.comb().

    @serhiy-storchaka serhiy-storchaka added 3.8 only security fixes stdlib Python modules in the Lib dir type-feature A feature request or enhancement labels Jun 1, 2019
    @rhettinger
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    +0 from me. It is inevitable that this will be requested now that we have comb(). The need for this is much less though.

    @mdickinson
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    +0 from me. It is inevitable that this will be requested now that we have comb().

    Exactly my thoughts, too. I don't think I'll have any use for math.perm; the main reason to add it will be to satisfy all those who got taught combinations and permutations at the same time, see them as a unit, and then get surprised when they find math.comb without math.perm.

    The good part is that now that we have math.comb, I think everything about the API of math.perm is already clear (including what to call it).

    @serhiy-storchaka
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    New changeset 5ae299a by Serhiy Storchaka in branch 'master':
    bpo-37128: Add math.perm(). (GH-13731)
    5ae299a

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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    @mdickinson @rhettinger @serhiy-storchaka