如何暗示同一子类的实例的同质列表？

Question

class A:
   pass 

class A1(A):
   pass

class A2(A):
   pass

def help_here(s: WHAT_SHOULD_I_TYPE_HERE ):
   # How to hint this function that accepts list,
   # where all elements should be instances of same subclass of A.
   # Example 1: [A1(), A1(), A1()] - good
   #            all components all elements are same class,
   #            and it is subclass of A
   # Example 2: [A2(), A2(), A2(), A2()] - valid. Same reason.
   # Example 3: [A1(), A1(), A2()] - invalid, not same classes.
   # Example 4: [1, 2] - invalid. Same class, but not subclass of A.

   if isinstance(s[0], A1):
       # If I use Union[List[A1], List[A2]] as type hint,
       # next line will have no warnings.
       # But if where will be List[A] then warning arrives:
       # Expected type 'List[A1]', got 'List[A]' instead.
       # It's Pycharm IDE.
       process_a1_list(s)


def process_a1_list(lst: List[A1]):
    pass


def another_test():
    # This is just to see, whether IDE will show warnings or not:

    # No warning should be on this block
    good_list: List[A1] = []
    help_here(good_list)
    
    # On both next calls IDE should warn 
    bad_list_1: List[A] = []
    help_here(bad_list_1)

    bad_list_2: List[int] = []
    help_here(bad_list_2)

我唯一的想法是：Union[List[A1], List[A2]]。

但是如果我不知道 的所有子类怎么办A？

有什么漂亮的方式来暗示吗？

更新：不太漂亮，但让 IDE (Pycharm) 按照我想要的方式检查类型。

Update2：我需要 IDE 类型提示解决方案而不是运行时检查。我不确定我想要的解决方案是否存在。

Python 3.8