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Optimize dict.__init__ and dict.update for dict argument #82400

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serhiy-storchaka opened this issue Sep 18, 2019 · 2 comments
Closed

Optimize dict.__init__ and dict.update for dict argument #82400

serhiy-storchaka opened this issue Sep 18, 2019 · 2 comments
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3.9 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) performance Performance or resource usage

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@serhiy-storchaka
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BPO 38219
Nosy @rhettinger, @methane, @serhiy-storchaka
PRs
  • bpo-38219: Optimize dict creating and updating by a dict. #16268
    		•

    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 2019-09-25.06:49:29.279>
created_at = <Date 2019-09-18.20:46:08.582>
labels = ['interpreter-core', '3.9', 'performance']
title = 'Optimize dict.__init__ and dict.update for dict argument'
updated_at = <Date 2019-09-25.06:49:29.278>
user = 'https://github.com/serhiy-storchaka'

    bugs.python.org fields:

    activity = <Date 2019-09-25.06:49:29.278>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2019-09-25.06:49:29.279>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2019-09-18.20:46:08.582>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 38219
keywords = ['patch']
message_count = 2.0
messages = ['352753', '353148']
nosy_count = 3.0
nosy_names = ['rhettinger', 'methane', 'serhiy.storchaka']
pr_nums = ['16268']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue38219'
versions = ['Python 3.9']
    @serhiy-storchaka
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    dict.__init__() and dict.update() with a positional argument look up the "keys" attribute of the argument to distinguish a mapping from a sequence of item-value pairs. It has a non-trivial cost. Merging dicts is optimized for exact dicts in PyDict_Merge(), so it would be worth to optimize also this check.

    $ ./python -m pyperf timeit -s "d = {}; D = dict" -- "D(d)"
Unpatched:  Mean +- std dev: 154 ns +- 4 ns
Patched:    Mean +- std dev: 110 ns +- 4 ns

$ ./python -m pyperf timeit -s "d = {}" -- "d.update(d)"
Unpatched:  Mean +- std dev: 112 ns +- 3 ns
Patched:    Mean +- std dev: 70.4 ns +- 1.5 ns

    The cost of the check is about 40 ns, and it is a significant part of the total time of creating/updating a small dict.

    @serhiy-storchaka serhiy-storchaka added 3.9 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) performance Performance or resource usage labels Sep 18, 2019
    @serhiy-storchaka
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    New changeset f163aea by Serhiy Storchaka in branch 'master':
    bpo-38219: Optimize dict creating and updating by a dict. (GH-16268)
    f163aea

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