在 Python 中訪問變量時運行代碼

Question

我有一個類人。 如果在 Person.sitting == True 時訪問了它的 running_speed 變量，則它必須拋出 SittingError。

class SittingError(Exception):
    pass

class Person:
    def __init__(self):
        self.sitting = False
        self.running_speed = 4

bob = Person()
print(bob.running_speed) # Works fine, he's not sitting
bob.sitting = True
print(bob.running_speed) # Throws SittingError, as running_speed was accessed while sitting

我該如何實現？

Answer 1

您可以使用@property裝飾器並在 getter 中拋出異常，如果sitting == true 。

class SittingError(Exception):
    pass

class Person:
    def __init__(self):
        self.sitting = False
        self._running_speed = 4

    @property
    def running_speed(self):
        if self.sitting:
            raise SittingError()
        return self._running_speed

    @running_speed.setter
    def running_speed(self, speed):
        self._running_speed = speed

bob = Person()
print(bob.running_speed) # Works fine, he's not sitting
bob.sitting = True
print(bob.running_speed)