the purpose of using protected attributes Python [duplicate]

Question

I'm learning Python, I've coded a bit in C++ before. I have simple very code:

class Car:
    def __init__(self, mark):
        self._mark = mark


class Bus:
    def __init__(self):
        self.audi = Car("Audi")

    def display(self):
        print(self.audi._mark)

def main():
    bmw = Car("BMW")
    print(bmw._mark)

    reno = Bus()
    reno.display()

main()

As far as I know in C++, only classes that inherit have access to "protected" attributes. So my questions:

• What is the purpose of using "protected" attributes / methods in Python?
• Why do I have access to the attribute _mark from the main function/class Bus?

Thank you for explain!