"AttributeError: 'ClassDef' object has no attribute 'value'" in _check_redefined_slots

[kainjow]

Bug description

I'm seeing this exception when a __slot__ is set to a list of enum values, but was able to reproduce minimally with just using a type as the list:

class MyClass:
    __slots__ = [str]

Configuration

No response

Command used

pylint test.py

Pylint output

Exception on node <ClassDef.MyClass l.1 at 0x7fe9152603d0> in file 'test.py'
Traceback (most recent call last):
  File "/Users/me/.virtualenvs/myvirtualenv/lib/python3.8/site-packages/pylint/utils/ast_walker.py", line 73, in walk
    callback(astroid)
  File "/Users/me/.virtualenvs/myvirtualenv/lib/python3.8/site-packages/pylint/checkers/classes/class_checker.py", line 804, in visit_classdef
    self._check_slots(node)
  File "/Users/me/.virtualenvs/myvirtualenv/lib/python3.8/site-packages/pylint/checkers/classes/class_checker.py", line 1369, in _check_slots
    self._check_redefined_slots(node, slots, values)
  File "/Users/me/.virtualenvs/myvirtualenv/lib/python3.8/site-packages/pylint/checkers/classes/class_checker.py", line 1385, in _check_redefined_slots
    slots_names.append(inferred_slot.value)
AttributeError: 'ClassDef' object has no attribute 'value'
************* Module box.sync.core.test
F0001(fatal):  1,0: : Fatal error while checking 'test.py'. Please open an issue in our bug tracker so we address this. There is a pre-filled template that you can use in '/Users/me/Library/Caches/pylint/pylint-crash-2022-04-01-11.txt'.

Expected behavior

pylint not crash.

Pylint version

pylint 2.13.4
astroid 2.11.2

OS / Environment

Python 3.8.8
macOS 11.6.4

Additional dependencies

No response

[jacobtylerwalls]

Thanks for the report. Regression in 56129b7. /CC @mbyrnepr2

[mbyrnepr2]

Thanks for the headsup. By the way, this example is invalid Python:

$ python example.py
Traceback (most recent call last):
  File "example.py", line 1, in <module>
    class MyClass:
TypeError: __slots__ items must be strings, not 'type'

But we probably want to avoid the crash either way.

[kainjow]

I’m on mobile now but I can update the example using enums which I think mapped to strings. Will check later.

[kainjow]

Enum example:

from enum import Enum

class MyEnum(Enum):
    VALUE = 'value'

class MyClass:
    __slots__ = [MyEnum.VALUE]

[mbyrnepr2]

Enum example:

from enum import Enum

class MyEnum(Enum):
    VALUE = 'value'

class MyClass:
    __slots__ = [MyEnum.VALUE]

Thanks for this example. This one is also invalid Python but I agree that we could tidy things up to prevent the crash report which happens when running Pylint on it.

Both of the examples provided emit the invalid-slots-object error so some of the heavy-lifting is already there to work on.
I'm happy to put together a MR for this.

python example2.py

Traceback (most recent call last):
  File "example2.py", line 6, in <module>
    class MyClass:
TypeError: __slots__ items must be strings, not 'MyEnum'

[kainjow]

Thanks. So I realized that enum example doesn't yet match the code base because the issues come from code that uses a custom Enum (added pre-Python 3). So in those cases, the value is a string, not an enum value.