mypy-guide-classes-1.py

from typing import List

class Stack:
    def __init__(self) -> None:
        self._values: List[int] = []

    def __repr__(self) -> str:
        return f'Stack{self._values!r}'
    
    def push(self, value: int) -> None:
        self._values.append(value)
    
    def pop(self) -> int:
        if len(self._values) == 0:
            raise RuntimeError('Underflow!')

        return self._values.pop()

stack = Stack()
print(stack)        # Stack[]

stack.push(2)
stack.push(10)
print(stack)        # Stack[2, 10]

print(stack.pop())  # 10
print(stack)        # Stack[2]