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Add key argument to heapq functions #46199

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gpolo mannequin opened this issue Jan 22, 2008 · 3 comments
Closed

Add key argument to heapq functions #46199

gpolo mannequin opened this issue Jan 22, 2008 · 3 comments
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@rhettinger
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stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@gpolo
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Mannequin

gpolo mannequin commented Jan 22, 2008

BPO 1904
Nosy @rhettinger
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  • heapq_key.py.patch: Adds key argument to heapq functions (C version not patched)
    		•

    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 = 'https://github.com/rhettinger'
closed_at = <Date 2008-03-24.08:13:40.503>
created_at = <Date 2008-01-22.10:54:02.209>
labels = ['type-bug', 'library']
title = 'Add key argument to heapq functions'
updated_at = <Date 2008-03-24.08:13:40.502>
user = 'https://bugs.python.org/gpolo'

    bugs.python.org fields:

    activity = <Date 2008-03-24.08:13:40.502>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2008-03-24.08:13:40.503>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2008-01-22.10:54:02.209>
creator = 'gpolo'
dependencies = []
files = ['9260']
hgrepos = []
issue_num = 1904
keywords = ['patch']
message_count = 3.0
messages = ['61496', '61497', '64397']
nosy_count = 2.0
nosy_names = ['rhettinger', 'gpolo']
pr_nums = []
priority = 'low'
resolution = 'rejected'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue1904'
versions = ['Python 2.6', 'Python 3.0']
    @gpolo
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    gpolo mannequin commented Jan 22, 2008

    Wouldn't it be useful to add a "key" argument to some heapq functions ?
    So you could construct a heap from dict items list based on the second
    item of each tuple, for example.

    @gpolo gpolo mannequin added stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Jan 22, 2008
    @gpolo
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    gpolo mannequin commented Jan 22, 2008

    Adding a simple patch that adds the "key" argument. To test this you
    need to comment lines where it tries to import the C version of heapq.

    @rhettinger
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    Rejecting the key-function patch in favor of the current typical
    approach of heapifying tuples that link a priority level with
    individual records. I've been a heavy user of the module and one of
    its principal maintainers. To date, I've seen very little need for key-
    function argument.

    Use cases aside, there is another design issue in that the key-function
    approach doesn't work well with the heap functions on regular lists.
    Successive calls to heap functions will of necessity call the key-
    function multiple times for any given element. This contrasts with sort
    () where the whole purpose of the key function was to encapsulate the
    decorate-sort-undecorate pattern which was desirable because the key-
    function called exactly once per element.

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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