Bad parsing of compiling regex with re.MULTILINE

[misha]

BPO	3587
Nosy	@pitrou

^{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 2008-08-18.13:25:09.890>
created_at = <Date 2008-08-18.12:02:22.428>
labels = ['expert-regex', 'type-bug', 'invalid']
title = 'Bad parsing of compiling regex with re.MULTILINE'
updated_at = <Date 2008-08-18.13:25:09.884>
user = 'https://bugs.python.org/misha'

bugs.python.org fields:

activity = <Date 2008-08-18.13:25:09.884>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2008-08-18.13:25:09.890>
closer = 'pitrou'
components = ['Regular Expressions']
creation = <Date 2008-08-18.12:02:22.428>
creator = 'misha'
dependencies = []
files = []
hgrepos = []
issue_num = 3587
keywords = []
message_count = 2.0
messages = ['71323', '71326']
nosy_count = 2.0
nosy_names = ['pitrou', 'misha']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue3587'
versions = ['Python 2.5', 'Python 2.4']

[misha]

import re
regex = r"[\w]+"

# Normal behaviour:
>>> re.findall(regex, "hello world", re.M)
['hello', 'world']
>>> re.compile(regex).findall("hello world")
['hello', 'world']

# Bug behaviour:
>>> re.compile(regex).findall("hello world", re.M)
['rld']

[pitrou]

The re.M flag is an attribute of the compiled pattern, and as such it
must be passed to compile(), not to findall().

These all work:

>>> re.compile(r"[a-z]+").findall("hello world")
['hello', 'world']
>>> re.compile(r"[a-z]+", re.M).findall("hello world")
['hello', 'world']
>>> re.compile(r"(?m)[a-z]+").findall("hello world")
['hello', 'world']

The second argument to the findall() method of compile objects is the
start position to match from (see
http://docs.python.org/lib/re-objects.html). This explains the behaviour
you are witnessing:

>>> re.M
8
>>> re.compile(r"[a-z]+").findall("hello world", 8)
['rld']