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re.sub does NOT substitute all the matching patterns when re.IGNORECASE is used #85830

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re.sub does NOT substitute all the matching patterns when re.IGNORECASE is used#85830
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3.8 (EOL)end of lifetopic-regextype-bugAn unexpected behavior, bug, or error

Description

@anitrajpurohit28
anitrajpurohit28
mannequin
opened on Aug 29, 2020
BPO 41664
Nosy @ezio-melotti

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 2020-08-29.22:32:24.365>
created_at = <Date 2020-08-29.21:47:33.268>
labels = ['expert-regex', 'invalid', 'type-bug', '3.8']
title = 're.sub does NOT substitute all the matching patterns when re.IGNORECASE is used'
updated_at = <Date 2020-08-29.22:32:24.364>
user = 'https://bugs.python.org/anitrajpurohit28'

bugs.python.org fields:

activity = <Date 2020-08-29.22:32:24.364>
actor = 'mrabarnett'
assignee = 'none'
closed = True
closed_date = <Date 2020-08-29.22:32:24.365>
closer = 'mrabarnett'
components = ['Regular Expressions']
creation = <Date 2020-08-29.21:47:33.268>
creator = 'anitrajpurohit28'
dependencies = []
files = []
hgrepos = []
issue_num = 41664
keywords = []
message_count = 2.0
messages = ['376083', '376086']
nosy_count = 3.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'anitrajpurohit28']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41664'
versions = ['Python 3.8']

Activity

  1. anitrajpurohit28 commented on Aug 29, 2020

    @anitrajpurohit28
    anitrajpurohit28mannequin
    on Aug 29, 2020
    MannequinAuthor

    Usage of re flags leads to inconsistent results when

    1. The pattern directly used in re.sub
    2. The pattern is re.compile'd and used

    Note 1: Input string is all in the lowercase 'all is fair in love and war'
    Note 2: Results are always consistent in case of re.compile'd pattern
    =======================================

    1. The pattern directly used in re.sub
      =======================================
    >>> import re
>>> re.sub(r'[aeiou]', '#', 'all is fair in love and war')
'#ll #s f##r #n l#v# #nd w#r'
>>> 
>>> re.sub(r'[aeiou]', '#', 'all is fair in love and war', re.IGNORECASE)
'#ll #s fair in love and war'
>>> 
>>> re.sub(r'[aeiou]', '#', 'all is fair in love and war', re.IGNORECASE|re.DOTALL)
'#ll #s f##r #n l#v# #nd w#r'
>>> 
>>>

    =======================================
    2. The pattern is re.compile'd and used
    =======================================

    >>> pattern = re.compile(r'[aeiou]', re.IGNORECASE)
>>> re.sub(pattern, '#', 'all is fair in love and war')
'#ll #s f##r #n l#v# #nd w#r'
>>> 
>>> pattern = re.compile(r'[aeiou]')
>>> re.sub(pattern, '#', 'all is fair in love and war')
'#ll #s f##r #n l#v# #nd w#r'
>>> 
>>> pattern = re.compile(r'[aeiou]', re.IGNORECASE | re.DOTALL)
>>> re.sub(pattern, '#', 'all is fair in love and war')
'#ll #s f##r #n l#v# #nd w#r'
  2. anitrajpurohit28
    added
    3.8 (EOL)end of life
    topic-regex
    type-bugAn unexpected behavior, bug, or error
    on Aug 29, 2020

  3. mrabarnett commented on Aug 29, 2020

    @mrabarnett
    mrabarnettmannequin
    on Aug 29, 2020
    Mannequin

    The 4th argument of re.sub is 'count', not 'flags'.

    re.IGNORECASE has the numeric value of 2, so:

        re.sub(r'[aeiou]', '#', 'all is fair in love and war', re.IGNORECASE)

    is equivalent to:

        re.sub(r'[aeiou]', '#', 'all is fair in love and war', count=2)
  4. mrabarnett
    closed this as completedon Aug 29, 2020
  5. mrabarnett
    added
    invalid
    on Aug 29, 2020
  6. mrabarnett
    closed this as completedon Aug 29, 2020
  7. mrabarnett
    added
    invalid
    on Aug 29, 2020
  8. ezio-melotti
    transferred this issue fromon Apr 10, 2022
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