class A:
    def __init__(self):
        self._X = 100
    def getX(self):
        return self._X
    def setX(self, wert):
        if wert < 0:
            return
        self._X = wert

a = A()
print(a.getX())
a.setX(300)
print(a.getX())
a.setX(-20)
print(a.getX())