在Python中访问变量时运行代码

Question

我有一个班上的人。如果在Person.siting==True时访问其running_speed变量，则它必须抛出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

我如何做到这一点

Answer 1

您可以使用@property修饰符，并在sitting == true时在getter中引发异常

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)