class Robot:
    def __init__(self, power):
        self.power = power
        
    power = property()
    
    @power.setter
    def power(self, value):
        if value < 0:
            self._power = 0
        else:
            self._power = value
            
    @power.getter
    def power(self):
        return self._power
        
wall_e = Robot(-100)
#wall_e.power = 20
print(wall_e.power)