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Optimize case-insensitive regular expressions #74471

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serhiy-storchaka opened this issue May 5, 2017 · 3 comments
Closed

Optimize case-insensitive regular expressions #74471

serhiy-storchaka opened this issue May 5, 2017 · 3 comments
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3.7 expert-regex performance stdlib

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@serhiy-storchaka
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@serhiy-storchaka serhiy-storchaka commented May 5, 2017

BPO 30285
Nosy @rhettinger, @ezio-melotti, @serhiy-storchaka
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  • #1482
  • 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/serhiy-storchaka'
    closed_at = <Date 2017-05-09.20:37:56.796>
    created_at = <Date 2017-05-05.17:02:59.161>
    labels = ['expert-regex', '3.7', 'library', 'performance']
    title = 'Optimize case-insensitive regular expressions'
    updated_at = <Date 2017-05-09.20:37:56.795>
    user = 'https://github.com/serhiy-storchaka'

    bugs.python.org fields:

    activity = <Date 2017-05-09.20:37:56.795>
    actor = 'serhiy.storchaka'
    assignee = 'serhiy.storchaka'
    closed = True
    closed_date = <Date 2017-05-09.20:37:56.796>
    closer = 'serhiy.storchaka'
    components = ['Library (Lib)', 'Regular Expressions']
    creation = <Date 2017-05-05.17:02:59.161>
    creator = 'serhiy.storchaka'
    dependencies = []
    files = []
    hgrepos = []
    issue_num = 30285
    keywords = []
    message_count = 3.0
    messages = ['293127', '293174', '293348']
    nosy_count = 4.0
    nosy_names = ['rhettinger', 'ezio.melotti', 'mrabarnett', 'serhiy.storchaka']
    pr_nums = ['1482']
    priority = 'normal'
    resolution = 'fixed'
    stage = 'resolved'
    status = 'closed'
    superseder = None
    type = 'performance'
    url = 'https://bugs.python.org/issue30285'
    versions = ['Python 3.7']

    @serhiy-storchaka
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    @serhiy-storchaka serhiy-storchaka commented May 5, 2017

    Matching and searching case-insensitive regular expressions is much slower than matching and searching case-sensitive regular expressions. Case-insensitivity requires converting every character in input string to lower case and disables some optimizations. But there are only 2669 cased characters (52 in ASCII mode). For all other characters in the pattern we can use case-sensitive matching.

    Results of microbenchmarks:

    $ ./python -m timeit -s "import re; p = re.compile(r'(?ai) +x'); s = ' '*10000+'x'"  "p.match(s)"
    Unpatched:  5000 loops, best of 5: 47.1 usec per loop
    Patched:    20000 loops, best of 5: 17.6 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'(?i) +x'); s = ' '*10000+'x'"  "p.match(s)"
    Unpatched:  2000 loops, best of 5: 109 usec per loop
    Patched:    20000 loops, best of 5: 17.6 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'(?ai)[ \t]+x'); s = ' '*10000+'x'"  "p.match(s)"
    Unpatched:  500 loops, best of 5: 537 usec per loop
    Patched:    5000 loops, best of 5: 84.2 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'(?i)[ \t]+x'); s = ' '*10000+'x'"  "p.match(s)"
    Unpatched:  500 loops, best of 5: 608 usec per loop
    Patched:    5000 loops, best of 5: 84.1 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'(?ai)/x'); s = ' '*10000+'/x'"  "p.search(s)"
    Unpatched:  1000 loops, best of 5: 226 usec per loop
    Patched:    20000 loops, best of 5: 13.4 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'(?i)/x'); s = ' '*10000+'/x'"  "p.search(s)"
    Unpatched:  1000 loops, best of 5: 284 usec per loop
    Patched:    20000 loops, best of 5: 13.4 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'(?ai)[/%]x'); s = ' '*10000+'/x'"  "p.search(s)"
    Unpatched:  500 loops, best of 5: 483 usec per loop
    Patched:    1000 loops, best of 5: 279 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'(?i)[/%]x'); s = ' '*10000+'/x'"  "p.search(s)"
    Unpatched:  500 loops, best of 5: 549 usec per loop
    Patched:    1000 loops, best of 5: 279 usec per loop

    The patch also optimizes searching some complex case-sensitive patterns. This is a side effect, I'll provide more comprehensive optimization in other issue.

    $ ./python -m timeit -s "import re; p = re.compile(r'([xy])'); s = ' '*10000+'x'"  "p.search(s)"
    Unpatched:  500 loops, best of 5: 633 usec per loop
    Patched:    1000 loops, best of 5: 250 usec per loop
    
    $ ./python -m timeit -s "import re; p = re.compile(r'((x|y)z)'); s = ' '*10000+'xz'"  "p.search(s)"
    Unpatched:  500 loops, best of 5: 716 usec per loop
    Patched:    1000 loops, best of 5: 250 usec per loop

    @serhiy-storchaka serhiy-storchaka self-assigned this May 5, 2017
    @serhiy-storchaka serhiy-storchaka added stdlib expert-regex performance labels May 5, 2017
    @rhettinger
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    @rhettinger rhettinger commented May 6, 2017

    This seems like a great idea.

    @serhiy-storchaka
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    @serhiy-storchaka serhiy-storchaka commented May 9, 2017

    New changeset 6d336a0 by Serhiy Storchaka in branch 'master':
    bpo-30285: Optimize case-insensitive matching and searching (bpo-1482)
    6d336a0

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