[New-bugs-announce] [issue41664] re.sub does NOT substitute all the matching patterns when re.IGNORECASE is used

[Anit Rajpurohit]

New submission from Anit Rajpurohit <anitrajpurohit28 at gmail.com>:

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'

----------
components: Regular Expressions
messages: 376083
nosy: anitrajpurohit28, ezio.melotti, mrabarnett
priority: normal
severity: normal
status: open
title: re.sub does NOT substitute all the matching patterns when re.IGNORECASE is used
type: behavior
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41664>
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