Weak deprecations for inline regular expression modifiers

[serhiy-storchaka]

BPO	30298
Nosy	@rhettinger, @ezio-melotti, @serhiy-storchaka
PRs	bpo-30298: Weaken the condition of deprecation warnings for inline modifiers. #1490 [3.6] bpo-30298: Weaken the condition of deprecation warnings for inline modifiers. (GH-1490) #1525

^{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 2017-05-10.03:44:51.484>
created_at = <Date 2017-05-07.14:39:18.298>
labels = ['expert-regex', 'type-bug', 'library', '3.7']
title = 'Weak deprecations for inline regular expression modifiers'
updated_at = <Date 2017-05-10.03:44:51.483>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2017-05-10.03:44:51.483>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2017-05-10.03:44:51.484>
closer = 'serhiy.storchaka'
components = ['Library (Lib)', 'Regular Expressions']
creation = <Date 2017-05-07.14:39:18.298>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 30298
keywords = []
message_count = 5.0
messages = ['293197', '293203', '293372', '293374', '293375']
nosy_count = 4.0
nosy_names = ['rhettinger', 'ezio.melotti', 'mrabarnett', 'serhiy.storchaka']
pr_nums = ['1490', '1525']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue30298'
versions = ['Python 3.6', 'Python 3.7']

[serhiy-storchaka]

There is a difference between handling inline modifiers in regular expressions between Python and all other regular expression engines that support inline modifiers. In other engines an inline modifier affect only the part of the pattern after it. It Python it affects also the part before it. For avoiding possible confusion and for removing this difference in distant future, using inline modifiers not at the start of the pattern was deprecated in 3.6 (see bpo-22493).

But the condition for raising a warning is too strong. It allows using '(?is)...', but '(?i)(?s)...' emits a warning. This makes hard modifying regular expressions by prefixing them with inline modifiers. This condition is unjustifiably strong because '(?i)(?s)...' doesn't have any ambiguity. It also disallows ' (?i)...' in verbose mode despite the fact that whitespaces are not significant in verbose mode.

Proposed patch weaks the condition of deprecation warnings. It allows using several subsequent inline modifiers at the start of the pattern and ignores whitespaces in verbose mode.

[rhettinger]

LGTM

[serhiy-storchaka]

New changeset 305ccbe by Serhiy Storchaka in branch 'master':
bpo-30298: Weaken the condition of deprecation warnings for inline modifiers. (bpo-1490)
305ccbe

[serhiy-storchaka]

New changeset 418d60a by Serhiy Storchaka in branch '3.6':
[3.6] bpo-30298: Weaken the condition of deprecation warnings for inline modifiers. (GH-1490) (bpo-1525)
418d60a

[serhiy-storchaka]

Thanks Raymond.