False positive too-few-public-methods when inheriting from a Generic class

[jindrahelcl]

Hi there, here's a bug in handling generics I discovered. (Somewhat related to #2568.)
When I try to inherit from a generic class (while fixing the type parameter), Pylint does not seem
to find the inherited methods. In the following example, if you remove the [int] part in the World class definition, it works as expected.

Steps to reproduce

# pylint: disable=no-self-use
from typing import Generic, TypeVar

MyGenericType = TypeVar("MyGenericType")

class Hello(Generic[MyGenericType]):

    def method1(self):
        return "hello"

    def method2(self):
        return "there"

    def method3(self):
        return "I have plenty of public methods"


class World(Hello[int]):
    def sole_method(self):
        return "I have methods from Hello also!"

Current behavior

Pylint reports:
test.py:17:0: R0903: Too few public methods (1/2) (too-few-public-methods)

Expected behavior

No error

pylint --version output

pylint 2.1.1
astroid 2.0.4
Python 3.6.6 (default, Sep 12 2018, 18:26:19) 
[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]]

[PCManticore]

Thanks for the report! pylint doesn't care too much about generics of typing constructs just yet, but we'll get there at some point.

[wshanks]

I think this may have been fixed. I don't reproduce it with the latest releases:

pylint 2.7.2
astroid 2.5.1
Python 3.9.2

[cdce8p]

I can't reproduce it either. We improved the handling of the typing module quite a bit in recent versions so I would assume this has been fixed. Going to close the issue.

If you still experience any problems, please report back and I'll reopen it.

[rkr87]

I'm seeing this issue when working with Pydantic, however, I'm not sure if it's a PyLint or a Pydantic issue.

I've have the classes below;

import re
from pathlib import Path
from typing import Generic, Iterator, Tuple, TypeVar
from pydantic import BaseModel, ConstrainedStr, Field
from pydantic.generics import GenericModel
from pydantic.types import NegativeInt

_KT = TypeVar('_KT', str, ConstrainedStr)
_VT = TypeVar('_VT')

class RootDictModel(GenericModel, Generic[_KT, _VT]):
    __root__: dict[_KT, _VT] = {}
    def __getitem__(self, key: _KT) -> _VT:
        return self.__root__[key]
    def __iter__(self) -> Iterator[_KT]:  # type: ignore
        return iter(self.__root__)
    def keys(self) -> list[_KT]:
        return list(self.__root__.keys())
    def values(self) -> list[_VT]:
        return list(self.__root__.values())
    def items(self) -> list[Tuple[_KT, _VT]]:
        return list(self.__root__.items())

class TagKey(ConstrainedStr):
    regex: re.Pattern[str] = re.compile(r'^\d*$')

class Tags(RootDictModel[TagKey, str]):
    ...

class Shortcut(BaseModel, extra='allow'):
    id: NegativeInt = Field(alias="appid")
    name: str = Field(alias="appname")
    exe: str = Field(alias="exe")
    dir: Path = Field(alias="StartDir")
    launch: str = Field("", alias="LaunchOptions")
    tags: Tags = Tags()

class Shortcuts(RootDictModel[str, Shortcut]):
    ...

class ShortcutsVDF(BaseModel):
    shortcuts: Shortcuts

Both Tags and Shortcuts result in Pylint giving a Too few public methods (0/2) pylint(too-few-public-methods) warning, despite the fact that there's three public methods in RootDictModel.

[Pierre-Sassoulas]

Can you try using pylint-pydantic to see if it fixes the issue ? If you find a reproducer without using pydantic it would help tremendously to troubleshoot this in pylint directly :)

[rkr87]

I've tried the pylint-pydantic plugin, which didn't help unfortunately. For now I've just disabled the pylint error in the lines affected.

I have tried a couple of different things to replicate the issue without using any pydantic models but haven't been able to, suggesting it probably is an interaction issue between pydantic and pylint.

[Pierre-Sassoulas]

I think opening an issue in pylint-pydantic is the thing to do at this point. We're relying on external plugin to handle libraries specificity now.