Bad behavior of re.IGNORECASE

[Janvec]

BPO	34048
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 2018-07-04.20:45:13.196>
created_at = <Date 2018-07-04.20:41:58.178>
labels = ['expert-regex', 'type-bug', 'invalid']
title = 'Bad behavior of re.IGNORECASE'
updated_at = <Date 2018-07-04.20:45:13.195>
user = 'https://bugs.python.org/Janvec'

bugs.python.org fields:

activity = <Date 2018-07-04.20:45:13.195>
actor = 'Jan \xc5\xa0vec'
assignee = 'none'
closed = True
closed_date = <Date 2018-07-04.20:45:13.196>
closer = 'Jan \xc5\xa0vec'
components = ['Regular Expressions']
creation = <Date 2018-07-04.20:41:58.178>
creator = 'Jan \xc5\xa0vec'
dependencies = []
files = []
hgrepos = []
issue_num = 34048
keywords = []
message_count = 2.0
messages = ['321062', '321063']
nosy_count = 3.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'Jan \xc5\xa0vec']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34048'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.6']

[Janvec]

re.sub() is behaving incorrectly, if re.IGNORECASE is used. Tested on 2.7, 3.4 and 3.6. The code follows:

import re

def subst(text):
   text = re.sub(r"\bnine\b", "niner", text, re.IGNORECASE)
   return text

print(subst("nine nine nine nine"))

It prints "niner niner nine nine". Without the re.IGNORECASE, the output is correct: "niner niner niner niner"

[Janvec]

Not a bug, it assigns the value of re.IGNORECASE into the count parameter. Sorry