Make the repr of re flags more readable

[serhiy-storchaka]

BPO	36548
Nosy	@ezio-melotti, @ethanfurman, @serhiy-storchaka
PRs	bpo-36548: Improve the repr of re flags. #12715

^{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 2019-06-10.08:02:04.009>
created_at = <Date 2019-04-07.10:28:01.405>
labels = ['expert-regex', '3.8', 'type-feature', 'library']
title = 'Make the repr of re flags more readable'
updated_at = <Date 2019-06-10.08:02:04.009>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2019-06-10.08:02:04.009>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-10.08:02:04.009>
closer = 'serhiy.storchaka'
components = ['Library (Lib)', 'Regular Expressions']
creation = <Date 2019-04-07.10:28:01.405>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 36548
keywords = ['patch']
message_count = 2.0
messages = ['339567', '344031']
nosy_count = 4.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'ethan.furman', 'serhiy.storchaka']
pr_nums = ['12715']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue36548'
versions = ['Python 3.8']

[serhiy-storchaka]

Currently the repr of re flags contains the name of the private class and it is not an evaluable expression:

>>> re.I
<RegexFlag.IGNORECASE: 2>
>>> re.I|re.S|re.X
<RegexFlag.VERBOSE|DOTALL|IGNORECASE: 82>

The repr of inverted flags is even more verbose:

<RegexFlag.ASCII|DEBUG|VERBOSE|UNICODE|DOTALL|MULTILINE|LOCALE|TEMPLATE: -3>
>>> ~(re.I|re.S|re.X)
<RegexFlag.ASCII|DEBUG|UNICODE|MULTILINE|LOCALE|TEMPLATE: -83>

The result of str() starves from the same issues.

>>> print(re.I)
RegexFlag.IGNORECASE
>>> print(re.I|re.S|re.X)
RegexFlag.VERBOSE|DOTALL|IGNORECASE
>>> print(~re.I)
RegexFlag.ASCII|DEBUG|VERBOSE|UNICODE|DOTALL|MULTILINE|LOCALE|TEMPLATE
>>> print(~(re.I|re.S|re.X))
RegexFlag.ASCII|DEBUG|UNICODE|MULTILINE|LOCALE|TEMPLATE

If the value contains unrecognized flags, it looks even more weird, and this information is not shown for invered flags:

>>> re.I|re.S|re.X|(1<<10)
<RegexFlag.1024|VERBOSE|DOTALL|IGNORECASE: 1106>
>>> ~(re.I|re.S|re.X|(1<<10))
<RegexFlag.ASCII|DEBUG|UNICODE|MULTILINE|LOCALE|TEMPLATE: -1107>
>>> print(re.I|re.S|re.X|(1<<10))
RegexFlag.1024|VERBOSE|DOTALL|IGNORECASE
>>> print(~(re.I|re.S|re.X|(1<<10)))
RegexFlag.ASCII|DEBUG|UNICODE|MULTILINE|LOCALE|TEMPLATE

This repr is also not consistent with the represenation of flags in the repr of the compiled pattern:

>>> re.compile('x', re.I|re.S|re.X)
re.compile('x', re.IGNORECASE|re.DOTALL|re.VERBOSE)

The proposed PR makes the repr be the same as for flags in the repr of the compiled pattern and represents inverted flags as the result of inversion:

>>> re.I
re.IGNORECASE
>>> re.I|re.S|re.X
re.IGNORECASE|re.DOTALL|re.VERBOSE
>>> ~re.I
~re.IGNORECASE
>>> ~(re.I|re.S|re.X)
~(re.IGNORECASE|re.DOTALL|re.VERBOSE)
>>> re.I|re.S|re.X|(1<<10)
re.IGNORECASE|re.DOTALL|re.VERBOSE|0x400
>>> ~(re.I|re.S|re.X|(1<<10))
~(re.IGNORECASE|re.DOTALL|re.VERBOSE|0x400)

__str__ is set to object.__str__, so that str() will return the same as repr().

[serhiy-storchaka]

New changeset 14a0e16 by Serhiy Storchaka in branch 'master':
bpo-36548: Improve the repr of re flags. (GH-12715)
14a0e16