re.match ignores optional flags when receiving a compiled regex pattern

[bcorfman]

BPO	1661
Nosy	@rhettinger

^{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 = 'https://github.com/rhettinger'
closed_at = <Date 2007-12-19.18:14:17.596>
created_at = <Date 2007-12-19.15:40:03.865>
labels = ['expert-regex', 'type-bug']
title = 're.match ignores optional flags when receiving a compiled regex pattern'
updated_at = <Date 2007-12-19.18:14:17.594>
user = 'https://bugs.python.org/bcorfman'

bugs.python.org fields:

activity = <Date 2007-12-19.18:14:17.594>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2007-12-19.18:14:17.596>
closer = 'rhettinger'
components = ['Regular Expressions']
creation = <Date 2007-12-19.15:40:03.865>
creator = 'bcorfman'
dependencies = []
files = []
hgrepos = []
issue_num = 1661
keywords = []
message_count = 2.0
messages = ['58808', '58816']
nosy_count = 2.0
nosy_names = ['rhettinger', 'bcorfman']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue1661'
versions = ['Python 2.6']

[bcorfman]

Python's documentation for the re.match function is match(pattern,
string, [flags]) where pattern can be either a regex string or a
compiled regex object. If it's a compiled regex object, then supplying
an optional flag to re.match (in my case, re.IGNORECASE) doesn't work
and, more to the point, fails silently. I think this should throw an
exception if it's not going to work.

See
http://mysite.verizon.net/bcorfman/2007/12/something-i-hate-about-pythons-re.html
for a discussion.

A possible change (proposed by effbot) is below:
Index: re.py
===================================================================

--- re.py       (revision 52330)
+++ re.py       (working copy)
@@ -224,6 +224,7 @@
         return p
     pattern, flags = key
     if isinstance(pattern, _pattern_type):
+        assert not flags
         return pattern
     if not sre_compile.isstring(pattern):
         raise TypeError, "first argument must be string or compiled
pattern"

[rhettinger]

Fixed. See commit 59573.