class Stack:
    def __init__(self) -> None:
        # Inicializa la estructura interna que almacena los elementos
        self.stack_list = []

    def push(self, value) -> None:
        # Agrega el valor al tope
        self.stack_list.append(value)

    def pop(self):
        # Retira y retorna el elemento del tope; retorna None si está vacío
        if self.stack_list != []:
            return self.stack_list.pop()
        return None 

    def is_empty(self) -> bool:
        # Retorna True si no hay elementos
        if self.stack_list == []:
            return True
        return False

def test_stack(operations: list) -> list:
    # Crea un Stack, ejecuta cada operación y acumula los resultados
    result = []
    stack = Stack()
    for operation in operations:
        if "push" in operation:
            stack.push(operation[1])
            result.append(None)
        elif "pop" in operation:
            result.append(stack.pop())
        elif "is_empty" in operation:
            result.append(stack.is_empty())
    return result