BytesWarning in re module when compiling certain bytes patterns

[JelleZijlstra]

BPO	30896
Nosy	@ezio-melotti, @serhiy-storchaka, @JelleZijlstra

^{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 2017-07-11.02:11:08.731>
created_at = <Date 2017-07-10.23:27:55.351>
labels = ['library']
title = 'BytesWarning in re module when compiling certain bytes patterns'
updated_at = <Date 2017-07-11.02:11:08.729>
user = 'https://github.com/JelleZijlstra'

bugs.python.org fields:

activity = <Date 2017-07-11.02:11:08.729>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2017-07-11.02:11:08.731>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2017-07-10.23:27:55.351>
creator = 'JelleZijlstra'
dependencies = []
files = []
hgrepos = []
issue_num = 30896
keywords = []
message_count = 2.0
messages = ['298095', '298100']
nosy_count = 3.0
nosy_names = ['ezio.melotti', 'serhiy.storchaka', 'JelleZijlstra']
pr_nums = []
priority = 'normal'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue30896'
versions = ['Python 3.6']

[JelleZijlstra]

This code in sre_parse (line 738 and down):

                        warnings.warn(
                            'Flags not at the start of the expression %s%s' % (
                                source.string[:20],  # truncate long regexes
                                ' (truncated)' if len(source.string) > 20 else '',
                            ),
                            DeprecationWarning, stacklevel=7
                        )

triggers a BytesWarning if you do _line_re = re.compile(br'^(.*?)$(?m)').

The fix should be simple; I can try to get a PR in over the next few days.

[serhiy-storchaka]

Thank you for your report Jelle, but this was fixed in bpo-30605.