在pygame中更改矩形位置

当游戏开始时,我正试图改变《异形入侵》中飞船的绘制位置,但我实际上不知道该在哪里进行更改。 我希望它在比赛开始时由我选择的位置,而不是中底。 船舶代码:

class Ship(Sprite):
"""A class to manage the ship."""

def __init__(self,ai_game):
    """Initialize the ship and set its starting position."""
    super().__init__()
    self.screen = ai_game.screen
    self.settings = ai_game.settings
    self.screen_rect = ai_game.screen.get_rect()

    #Load the ship image and get its rect.
    self.image = pygame.image.load('images/ship.png')
    self.rect = self.image.get_rect()

    #Start each new ship at the bottom center of the screen.
    self.rect.midbottom = self.screen_rect.midbottom

    #Store a decimal value for the ship's horizontal position.
    self.x = float(self.rect.x)
    self.y = float(self.rect.y)

    #Movement flags
    self.moving_right = False
    self.moving_left = False
    self.moving_up = False
    self.moving_down = False

def update(self):
    """Update the ship's position based on the movement flags."""
    #Update the ship's x value, not the rect.
    if self.moving_right and self.rect.right < self.screen_rect.right:
        self.x += self.settings.ship_speed
    if self.moving_left and self.rect.left > 0:
        self.x -= self.settings.ship_speed
    if self.moving_up and self.rect.top > 0:
        self.y -= self.settings.ship_speed
    if self.moving_down and self.rect.bottom <= self.screen_rect.bottom:
        self.y += self.settings.ship_speed


    #Update rect object from self.x.
    self.rect.x = self.x
    self.rect.y = self.y
        

def blitme(self):
        """Draw the ship at its current location."""
        self.screen.blit(self.image, self.rect)

def center_ship(self):
    """Center the ship on the screen."""
    self.rect.midbottom = self.screen_rect.midbottom
    self.x = float(self.rect.x)
    self.y = float(self.rect.y)