Variable Types in a class

[Yoriz]

If you are actively using a type checker the following code would flag an error

from dataclasses import dataclass
from typing import Optional


@dataclass
class Node:
    value: float
    next: Optional["Node"] = None
    prev: Optional["Node"] = None


node = Node(0.1)
node.string = "Hello"

For instance in vscode with the type checker mode set to at least basic, pylance would put a red line under string and hovering over it would show the following:

Error:
string: Literal['Hello']
Cannot assign member "string" for type "Node"
  Member "string" is unknown

---

Python version 3.10 added slots as a parameter to dataclass, The following can now be done

from dataclasses import dataclass
from typing import Optional


@dataclass(slots=True)
class Node:
    value: float
    next: Optional["Node"] = None
    prev: Optional["Node"] = None


node = Node(0.1)
node.string = "Hello"

this will give the same AttributeError: 'Node' object has no attribute 'string' error