AttributeError when copying flags in the `re` module.

[pschanely]

Bug report

In CPython 3.11, I've noticed that an attempt to copy (combined) regular expression flags fails with an attribute error; like so:

>>> import copy, re
>>> copy.copy(re.A | re.I)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "lib/python3.11/copy.py", line 102, in copy
    return _reconstruct(x, None, *rv)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "lib/python3.11/copy.py", line 265, in _reconstruct
    y = func(*args)
        ^^^^^^^^^^^
  File "lib/python3.11/enum.py", line 862, in __getattr__
    raise AttributeError(name) from None
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: ASCII|IGNORECASE

Your environment

• CPython versions tested on: 3.11.0b3
• Operating system and architecture: macOS 10.15.7

Background

This behavior was detected from a CrossHair test failure here, in which we realize possibly symbolic arguments prior to regex compilation. (it's an esoteric use case, and I expect not very high priority)

[JelleZijlstra]

Thanks for reporting! Confirmed that copy.copy(re.A | re.I) fails on 3.11 but works on 3.10. Marking as a release blocker since this is a regression.

cc @ethanfurman for enums

[JelleZijlstra]

Also repros with enum.IntFlag directly:

$ ./python.exe
Python 3.11.0b3+ (heads/3.11:7aa4038a6e, Jun 14 2022, 09:35:10) [Clang 13.0.0 (clang-1300.0.29.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import copy, enum
>>> class F(enum.IntFlag):
...     a = 2
...     b = 4
... 
>>> copy.copy(F.a | F.b)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/jelle/py/cpython/Lib/copy.py", line 102, in copy
    return _reconstruct(x, None, *rv)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jelle/py/cpython/Lib/copy.py", line 265, in _reconstruct
    y = func(*args)
        ^^^^^^^^^^^
  File "/Users/jelle/py/cpython/Lib/enum.py", line 862, in __getattr__
    raise AttributeError(name) from None
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: a|b

[dignissimus]

Also occurs on 3.12

[tiran]

In 3.11 the __reduce__ and __reduce_ex__ methods returns different values:

# 3.10
>>> import re
>>> flags = re.I | re.A
>>> flags.__reduce__()
(<function _reconstructor at 0x7f58bb775ea0>, (<enum 'RegexFlag'>, <class 'int'>, 258), {'_name_': None, '_value_': 258})
>>> flags.__reduce_ex__(1)
(<enum 'RegexFlag'>, (258,))
>>> flags._name_ is None
True
>>> flags.name is None
True

# 3.11
>>> import re
>>> flags = re.I | re.A
>>> flags.__reduce__()
(<function _reconstructor at 0x7fd0b8d4f920>, (<flag 'RegexFlag'>, <class 'int'>, 258), {'_value_': 258, '_name_': 'ASCII|IGNORECASE'})
>>> flags.__reduce_ex__(1)
(<built-in function getattr>, (<flag 'RegexFlag'>, 'ASCII|IGNORECASE'))
>>> flags._name_
'ASCII|IGNORECASE'
>>> flags.name
'ASCII|IGNORECASE'

[tiran]

I guess the regression was introduced by GH-26658 and commit 62f1d2b .

A quick fix would be to reduce flags by value instead of by name.

class Flag(Enum, boundary=STRICT):
    def __reduce_ex__(self, proto):
        return self.__class__, (self._value_, )

[dignissimus]

Running the example in 0507303 so works fine, so commit 62f1d2b introduced the issue

[dignissimus]

Oh, it looks like we came across it at the same time 😂