What is the best way for a class definition with PEP 526

Lets say I have a class like below:

Class Foo:
    x: int
    y: List[int]
    z: int = 5

    def __init__(self, x:int, z: int = 5):
        self.x = x
        self.y = []
        self.z = z

   ### some other methods

My questions are;

1. If I am using the types inside the init function, isn’t me using types at the class level become redundant?

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2. I want the variable y to be initialized to an empty list for each instance. So, I didn’t write the below code as it initialized the y at the class level. Is my understanding correct?

   Class Foo:
      x: int
      y: List[int] = []
      z: int = 5
   
      def __init__(self, x:int, z: int = 5):
          self.x = x
          self.z = z
   

I’m trying to improve my code quality, so if I am missing some primary understanding regarding it, please let me know.

Thank you in advance.

>Solution :

Class-level type hints are still helpful — they’re good for documentation and static analysis, even if you also use them elsewhere.

Initializing mutable types like y inside init helps avoid shared state between instances, avoiding bugs that can be hard to track down.

Your current implementation is good practice re: 526

Sources:

My articles: https://ioflood.com/blog/python-type-hints/ and https://ioflood.com/blog/mutable-vs-immutable-in-python-object-data-types-explained/#Dangers_of_using_mutable_default_arguments