Some RegexFlag cannot be printed in the repr

[pablogsal]

BPO	44929
Nosy	@ethanfurman, @ambv, @pablogsal
PRs	bpo-44929: Fix enum string representation in the REPL #27789

^{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 2021-08-27.10:09:44.917>
created_at = <Date 2021-08-16.22:03:59.743>
labels = ['3.11']
title = 'Some RegexFlag cannot be printed in the repr'
updated_at = <Date 2021-08-27.10:09:44.917>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2021-08-27.10:09:44.917>
actor = 'lukasz.langa'
assignee = 'none'
closed = True
closed_date = <Date 2021-08-27.10:09:44.917>
closer = 'lukasz.langa'
components = []
creation = <Date 2021-08-16.22:03:59.743>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 44929
keywords = ['patch']
message_count = 8.0
messages = ['399688', '399690', '399691', '399692', '399827', '399863', '400271', '400408']
nosy_count = 3.0
nosy_names = ['ethan.furman', 'lukasz.langa', 'pablogsal']
pr_nums = ['27789']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue44929'
versions = ['Python 3.11']

[pablogsal]

When printing some instance of RegexFlag **in the REPL** it fails to print:

>>> import gc
# This prints a ton of objects, including the bad enum RegexFlag one
>>> gc.get_referrers(None) 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pablogsal/github/cpython/Lib/enum.py", line 1399, in global_flag_repr
    return "%x" % (module, cls_name, self._value_)
           ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
TypeError: %x format: an integer is required, not str

[pablogsal]

(Deleted last message because it was incorrect)

[pablogsal]

Simpler reproducer:

>>> import re
>>> re.RegexFlag(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pablogsal/github/cpython/Lib/enum.py", line 1399, in global_flag_repr
    return "%x" % (module, cls_name, self._value_)
           ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
TypeError: %x format: an integer is required, not str

[pablogsal]

This looks incorrect:

cpython/Lib/enum.py

Line 1399 in 1512bc2

return "%x" % (module, cls_name, self._value_)

[ambv]

Ethan, could you take a look at the PR? I added a few failing test methods since repr handling for global enum flags wasn't covered and looks unfinished. If you tell us what the expected return values should be, I'll finish the fix.

[ethanfurman]

_name_ is only None if the entire enum value is outside any named member and _boundary_ is KEEP -- so

    class Example(Flag, boundary=KEEP):
        first = auto()
        second = auto()
        third = auto()

    >>> Example(0)
    module.Example(0)

    >>> Example(8)
    module.Example(8)

No need to backport.

[ethanfurman]

New changeset 24da544 by Pablo Galindo Salgado in branch 'main':
bpo-44929: [Enum] Fix global repr (GH-27789)
24da544

[ambv]

repr(re.RegexFlag(0)) no longer crashes so we can close this.