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re.IGNORECASE does not match literal "_" (underscore) #56156
Description
| BPO | 11947 |
|---|---|
| Nosy | @pitrou, @ezio-melotti |
| Superseder |
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 2011-04-28.20:49:19.294>
created_at = <Date 2011-04-28.17:02:55.958>
labels = ['expert-regex', 'type-bug']
title = 're.IGNORECASE does not match literal "_" (underscore)'
updated_at = <Date 2014-10-29.16:15:11.230>
user = 'https://bugs.python.org/RobM'bugs.python.org fields:
activity = <Date 2014-10-29.16:15:11.230>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2011-04-28.20:49:19.294>
closer = 'ezio.melotti'
components = ['Regular Expressions']
creation = <Date 2011-04-28.17:02:55.958>
creator = 'RobM'
dependencies = []
files = []
hgrepos = []
issue_num = 11947
keywords = []
message_count = 6.0
messages = ['134700', '134716', '134717', '134723', '134752', '134831']
nosy_count = 5.0
nosy_names = ['effbot', 'pitrou', 'ezio.melotti', 'mrabarnett', 'RobM']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '11957'
type = 'behavior'
url = 'https://bugs.python.org/issue11947'
versions = ['Python 2.6']
Activity
RobM commentedon Apr 28, 2011
Regular expressions which are written match literal underscores ("_", ASCII
ordinal 95) and specify
re.IGNORECASEduring compilation do not consistentlymatch underscores: it seems some occurrences are matched, but others are not.
The following session log shows the problem:
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import re >>> subject = "[Conclave-Mendoi]_ef_-_a_tale_of_memories_00-12_H264" >>> print subject.encode("base64") # Incase my environment encoding is to blame W0NvbmNsYXZlLU1lbmRvaV1fZWZfLV9hX3RhbGVfb2ZfbWVtb3JpZXNfMDAtMTJfSDI2NA== >>> re.sub("_", "X", subject) # No flags, does what I expect '[Conclave-Mendoi]XefX-XaXtaleXofXmemoriesX00-12XH264' >>> >>> re.sub("_", "X", subject, re.IGNORECASE) # Misses some matches '[Conclave-Mendoi]XefX-_a_tale_of_memories_00-12_H264' >>> >>> re.sub("_", "X", subject, re.IGNORECASE | re.LOCALE) # Misses fewer matches '[Conclave-Mendoi]XefX-XaXtaleXofXmemories_00-12_H264' >>> >>> re.sub("_", "X", subject, re.IGNORECASE | re.LOCALE | re.UNICODE) # Works OK '[Conclave-Mendoi]XefX-XaXtaleXofXmemoriesX00-12XH264' >>> >>> re.sub("_", "X", subject, re.IGNORECASE | re.UNICODE) # Works OK '[Conclave-Mendoi]XefX-XaXtaleXofXmemoriesX00-12XH264' >>> >>> type(subject) # Don't think this is a unicode string <type 'str'> >>>Since my
subjectvariable is of typestrand only contains ASCII charactersI do not believe that the
re.UNICODEflag should be required.mrabarnett commentedon Apr 28, 2011
help(re.sub) says:
and re.IGNORECASE has a value of 2.
Therefore this:
is telling it to replace at most 2 occurrences of "_".
ezio-melotti commentedon Apr 28, 2011
Closing as invalid.
I wonder if it would be better to have count as a keyword-only argument though, since this problem seems to come up pretty often and it's not easy to debug.
mrabarnett commentedon Apr 28, 2011
I don't know how much code that might break. It might not be that much; I can't remember when I last used re.sub without the default count.
RobM commentedon Apr 29, 2011
Oh, that's embarrassing. :-)
Could a type-check be used to alert the user to their mistake? I suppose that would require re.IGNORECASE (et al) to be of some new type (presumably sub-classed from Integer).
(Thanks for the quick response, and sorry to waste your time)
ezio-melotti commentedon Apr 30, 2011
See also bpo-11957.