re.finditer behaviour in re.MULTILINE mode fails to match first 7 characters

[tdawes]

BPO	34873
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 2018-10-02.21:32:07.630>
created_at = <Date 2018-10-02.21:29:14.486>
labels = ['expert-regex', '3.8', 'type-bug', '3.7', 'invalid']
title = 're.finditer behaviour in re.MULTILINE mode fails to match first 7 characters'
updated_at = <Date 2018-10-02.21:32:07.628>
user = 'https://bugs.python.org/tdawes'

bugs.python.org fields:

activity = <Date 2018-10-02.21:32:07.628>
actor = 'tdawes'
assignee = 'none'
closed = True
closed_date = <Date 2018-10-02.21:32:07.630>
closer = 'tdawes'
components = ['Regular Expressions']
creation = <Date 2018-10-02.21:29:14.486>
creator = 'tdawes'
dependencies = []
files = []
hgrepos = []
issue_num = 34873
keywords = []
message_count = 2.0
messages = ['326911', '326912']
nosy_count = 3.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'tdawes']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34873'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5', 'Python 3.6', 'Python 3.7', 'Python 3.8']

[tdawes]

re.finditer appears to fail to match within the first 7 characters in a string when re.MULTILINE is used:

>>> REGEX = re.compile("y")
>>> [list(m.start() for m in REGEX.finditer("{}y".format("x"*i), re.MULTILINE)) for i in range(10)]
[[], [], [], [], [], [], [], [], [8], [9]]

Without re.MULTILINE, this works fine:

>>> [list(m.start() for m in REGEX.finditer("{}y".format("x"*i))) for i in range(10)]
[[0], [1], [2], [3], [4], [5], [6], [7], [8], [9]]

Passing re.MULTILINE to re.compile doesn't seem to have any effect.

[tdawes]

Please ignore, re.finditer and REGEX.finditer aren't the same. I was passing re.MULTILINE (= 8) to endPos.