在Python <arcade库>

Question

我目前正在某种作业中编码。 我创建了一个名为Ship的类，并创建了一些方法来使对象类ship能够移动。

class Ship():
def __init__(self):
    self.center.x = 400
    self.center.y = 300
    self.velocity.dx = .25
    self.velocity.dy = .25

def advance_down(self):

    self.center.y = self.center.y - self.velocity.dy

这是我的代码

def check_keys(self):
"""
    This function checks for keys that are being held down.
    You will need to put your own method calls in here.
    """
        if arcade.key.DOWN in self.held_keys:
            self.ship1.advance_down()

前进仅改变位置

    def on_key_press(self, key: int, modifiers: int):
    """
    Puts the current key in the set of keys that are being held.
    You will need to add things here to handle firing the bullet.
    """
            if key == arcade.key.DOWN:
               self.held_keys.add(key)

这会将当前按下的键添加到self.held_keys集中。 我正在打电话给正子。

 def update(self, delta_time):
    """
    Update each object in the game.
    :param delta_time: tells us how much time has actually elapsed
    ""

    self.ship1.advance_down()

当我运行代码时，我能够很好地显示所有内容，但是一旦按下按键，它什么也没做。 有什么想法吗？