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MULTILINE confuses re.split #59742

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MULTILINE confuses re.split#59742
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topic-regextype-bugAn unexpected behavior, bug, or error

Description

@dabrahams
dabrahams
mannequin
opened on Aug 2, 2012
BPO 15537
Nosy @ezio-melotti, @dabrahams, @serhiy-storchaka
Superseder
  • bpo-11957: re.sub confusion between count and flags args
    		•

    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 2012-08-03.02:41:48.843>
created_at = <Date 2012-08-02.14:58:56.855>
labels = ['expert-regex', 'type-bug']
title = 'MULTILINE confuses re.split'
updated_at = <Date 2014-10-29.16:13:16.748>
user = 'https://github.com/dabrahams'

    bugs.python.org fields:

    activity = <Date 2014-10-29.16:13:16.748>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2012-08-03.02:41:48.843>
closer = 'ezio.melotti'
components = ['Regular Expressions']
creation = <Date 2012-08-02.14:58:56.855>
creator = 'dabrahams'
dependencies = []
files = []
hgrepos = []
issue_num = 15537
keywords = []
message_count = 5.0
messages = ['167228', '167240', '167243', '167282', '167283']
nosy_count = 4.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'dabrahams', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '11957'
type = 'behavior'
url = 'https://bugs.python.org/issue15537'
versions = ['Python 2.7']

    Activity

    1. dabrahams commented on Aug 2, 2012

      @dabrahams
      dabrahamsmannequin
      on Aug 2, 2012
      MannequinAuthor

      compare the output of

      $ python -c "open('/tmp/tst','w').write(100*'x\n');import re;print len(re.split('\n(?=x)', open('/tmp/tst').read()))"
100

      with

      $ python -c "open('/tmp/tst','w').write(100*'x\n');import re;print len(re.split('\n(?=x)', open('/tmp/tst').read(), re.MULTILINE))"
9
    2. dabrahams
      added
      topic-regex
      on Aug 2, 2012

    3. serhiy-storchaka commented on Aug 2, 2012

      @serhiy-storchaka
      serhiy-storchaka
      on Aug 2, 2012
      Member
      re.split = split(pattern, string, maxsplit=0, flags=0)
    Split the source string by the occurrences of the pattern,
    returning a list containing the resulting substrings.  If
    capturing parentheses are used in pattern, then the text of all
    groups in the pattern are also returned as part of the resulting
    list.  If maxsplit is nonzero, at most maxsplit splits occur,
    and the remainder of the string is returned as the final element
    of the list.

maxsplit=0 in your fist example and maxsplit=8 (re.MULTILINE is 8) in your second example. This is not a bug, this is a wrong understanding.

    4. mrabarnett commented on Aug 2, 2012

      @mrabarnett
      mrabarnettmannequin
      on Aug 2, 2012
      Mannequin

      There are actually 2 issues here:

      1. The third argument is 'maxsplit', the fourth is 'flags'.

      2. It never splits on a zero-width match. See bpo-3262.

    5. ezio-melotti commented on Aug 3, 2012

      @ezio-melotti
      ezio-melotti
      on Aug 3, 2012
      Member

      See also bpo-11957.

    6. ezio-melotti
      added
      invalid
      on Aug 3, 2012
    7. ezio-melotti
      closed this as completedon Aug 3, 2012
    8. ezio-melotti
      added
      type-bugAn unexpected behavior, bug, or error
      on Aug 3, 2012

    9. dabrahams commented on Aug 3, 2012

      @dabrahams
      dabrahamsmannequin
      on Aug 3, 2012
      MannequinAuthor

      Dang! Thanks, and sorry for wasting everyone's time on this.

    10. vstinner
      removed
      invalid
      on Oct 29, 2014
    11. ezio-melotti
      transferred this issue fromon Apr 10, 2022
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