Given a class `A` that overloads `__getattr__`

```
class A:
  def __getattr__(self, key):
    return 0
```

An instance of this class is always identified as a dataclass.

```
from dataclasses import is_dataclass

a = A()
print(is_dataclass(a))
```

gives the output `True`.

Possible fix: check for the instance type.

```
is_dataclass(type(a))
```

does give the correct answer.