False-positive unused-private-member with class name

[cdce8p]

Steps to reproduce

class Singleton:
    __instance = None

    @staticmethod
    def instance():
        if Singleton.__instance is None:
            Singleton()
        return Singleton.__instance

    def __init__(self):
        try:
            Singleton.__instance = 42  # Error here
        except Exception:  # pylint: disable=broad-except
            print("Error")
            Singleton.__instance = False  # Error here

or

class Singleton:
    __instance = None

    @classmethod  # Use class method here
    def instance(cls):
        if cls.__instance is None:
            cls()
        return cls.__instance

    def __init__(self):
        try:
            Singleton.__instance = 42  # Error here
        except Exception:  # pylint: disable=broad-except
            print("Error")
            Singleton.__instance = False  # Error here

Current behavior

test.py:12:12: W0238: Unused private member `Singleton.__instance` (unused-private-member)
test.py:15:12: W0238: Unused private member `Singleton.__instance` (unused-private-member)

Expected behavior

No errors

pylint --version output

pylint 2.9.4-dev0
astroid 2.6.3-dev0
Python 3.10.0b3

Additional information

Probably needs to be fixed similar to #4663

[cdce8p]

@yushao2 Would you like to take a look at that?

[yushao2]

@yushao2 Would you like to take a look at that?

Sure thing.

I don't really use classes that much, but just wanted to ask if there might be cases when a superclass's class name is used too

e.g.

class Singleton:
    __instance = None

    @staticmethod
    def instance():
        if Singleton.__instance is None:
            Singleton()
        return Singleton.__instance

    def __init__(self):
        try:
            Singleton.__instance = 42  # Error here
        except Exception:  # pylint: disable=broad-except
            print("Error")
            Singleton.__instance = False  # Error here

class InheritingClass(Singleton):
    def test(self):
        Singleton.__instance

Not sure if this is even valid syntax, but just wanted some clarifications at this stage before I start working on it

[Pierre-Sassoulas]

As __instance is private in Singleton you should not be able to access it from InheritingClass

[yushao2]

As __instance is private in Singleton you should not be able to access it from InheritingClass

right... not sure why my brain wasn't working. thank you 🙏

[yushao2]

@cdce8p

picking this up after a hiatus, see #4782

[cdce8p]

@cdce8p

picking this up after a hiatus, see #4782

I'll be sure to take a look!

[stanislavlevin]

The second example in this issue hasn't been fixed with the mentioned PR (today's main).

[builder@localhost BUILD]$ python3 -m pylint --version
pylint 2.10.0-dev0
astroid 2.6.5
Python 3.9.6 (default, Jun 29 2021, 10:42:27) 
[GCC 10.2.1 20210313 (ALT Sisyphus 10.2.1-alt3)]

[stanislavlevin]

[builder@localhost BUILD]$ python3 -m pylint a.py
************* Module a
a.py:12:12: W0238: Unused private member `Singleton.__instance` (unused-private-member)
a.py:15:12: W0238: Unused private member `Singleton.__instance` (unused-private-member)

[yushao2]

@stanislavlevin hey thanks, I'll try it out and investigate