false negative with dangerous-default-value

[dpinol]

Bug description

# pylint: disable=missing-module-docstring
from dataclasses import dataclass
# pylint: disable=missing-class-docstring
# pylint: disable=too-few-public-methods
class Arg:
    def __init__(self):
        self.field = 4


@dataclass(frozen=True)
class Frozen:
    field: int = 3


# pylint: disable=missing-function-docstring
def func(arg=Arg()):
    arg.field = 5


# pylint: disable=missing-function-docstring
def func2(frozen=Frozen()):
    print(frozen.field)

Configuration

No response

Command used

pylint kk.py

Pylint output

-------------------------------------------------------------------
Your code has been rated at 10.00/10 (previous run: 8.00/10, +2.00)

Expected behavior

ttbomk it should report dangerous-default-value for func, but not for func2 since the argument is readonly.

Pylint version

pylint 2.17.4
astroid 2.15.5
Python 3.11.3 (main, May  2 2023, 16:42:49) [GCC 11.3.0]

OS / Environment

ubuntu 22.10

Additional dependencies

No response

[jacobtylerwalls]

Thanks for the report! IMO this is a duplicate of #4659. Please feel free to review the PR for it and offer a view on moving it forward.

[dpinol]

Hi, thanks for the quick answer.
IMO #4659 is different because it refers to immutable stateful objects.
What I mean is that dangerous-default-value refers to "a mutable value as list or dictionary". If "dangerous-default-value" is only meant for dicts and lists, I think the documentation should be more explicit to say instead "list or dictionary"

[jacobtylerwalls]

IMO #4659 is different because it refers to immutable stateful objects.

As I read #4659 it was suggesting collapsing the distinction between "mutable" and "stateful", not introducing a distinctive "immutable stateful" class.

In other words, suggesting expanding the message beyond dicts and lists to callables that we can reasonably detect return something other than a constant. Here, you have a callable Arg returning a dataclass instance, which isn't a constant. A frozen dataclass would be like a constant, so I left a comment to that effect.

If "dangerous-default-value" is only meant for dicts and lists, I think the documentation should be more explicit to say instead "list or dictionary"

Did you mean if "is not only meant"? Yes, the docs would need to be updated as part of that PR.