pygame 2维移动敌人向玩家移动，如何计算x和y速度？

import pygame
import math

# 初始化Pygame
pygame.init()

# 设置屏幕大小
screen_width = 800
screen_height = 600
screen = pygame.display.set_mode((screen_width, screen_height))

# 玩家和敌人的初始位置
player_pos = [400, 300]
enemy_pos = [100, 100]

# 敌人的移动速度
enemy_speed = 2

# 游戏循环
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    # 计算方向向量
    direction_vector = [player_pos[0] - enemy_pos[0], player_pos[1] - enemy_pos[1]]

    # 计算向量的长度
    length = math.sqrt(direction_vector[0]**2 + direction_vector[1]**2)

    # 归一化方向向量并乘以速度
    if length != 0:
        enemy_speed_vector = [direction_vector[0] / length * enemy_speed, direction_vector[1] / length * enemy_speed]
    else:
        enemy_speed_vector = [0, 0]

    # 更新敌人的位置
    enemy_pos[0] += enemy_speed_vector[0]
    enemy_pos[1] += enemy_speed_vector[1]

    # 清屏并绘制玩家和敌人
    screen.fill((0, 0, 0))
    pygame.draw.circle(screen, (255, 0, 0), player_pos, 20)
    pygame.draw.circle(screen, (0, 255, 0), enemy_pos, 20)

    # 更新屏幕
    pygame.display.flip()

# 退出Pygame
pygame.quit()