[Python知识库]类函数注意return与print

class Car():
    def __init__(self,make,model,year):
        self.make=make
        self.model=model
        self.year=year
        self.odometer_reading = 0
    def get_descriptive_name(self):
        print(self.make+" "+self.model+" "+str(self.year))
    def read_odometer(self):
        print("This car has "+self.odometer_reading+" mails on it.")

class Battery():
    def __init__(self,battery_size=70):
        self.battery_size=battery_size

    def describe_battery(self):
        print("The car has "+str(self.battery_size)+" -kWh battery.")

class ElectricCar(Car):
    def __init__(self,make,model,year):
        super().__init__(make,model,year)
        self.battery=Battery()

my_new_car=ElectricCar('we','vee',2013)
print(my_new_car.get_descriptive_name())##注意看get_descriptive_name()函数本来就输出，print（print）
my_new_car.battery.describe_battery()

所以结果会多一个None