for fish in fish_list: fish_pos=Vector2(fish[2],fish[3]) distanse2 = sp - fish_pos if distanse2.length() <= 50: img_fish = pygame.transform.rotozoom(img_fish, 0, 1.1) fish_list.remove(fish)需要怎样改写出大鱼吃小鱼碰撞代码，详细注释

以下是一个简单的大鱼吃小鱼碰撞代码，详细注释：

import pygame
from pygame.math import Vector2

# 初始化pygame
pygame.init()

# 设置屏幕大小
screen_width = 640
screen_height = 480
screen = pygame.display.set_mode((screen_width, screen_height))
pygame.display.set_caption("大鱼吃小鱼")

# 加载图片
img_fish_big = pygame.image.load("fish_big.png").convert_alpha()
img_fish_small = pygame.image.load("fish_small.png").convert_alpha()

# 定义鱼的类
class Fish:
    def __init__(self, pos, img):
        self.pos = pos
        self.img = img
        self.rect = img.get_rect(center=pos)
        self.speed = Vector2(0, 0)
    
    def update(self):
        # 移动鱼
        self.pos += self.speed
        self.rect.center = self.pos
        
        # 限制鱼在屏幕范围内
        if self.rect.left < 0:
            self.rect.left = 0
            self.speed.x *= -1
        elif self.rect.right > screen_width:
            self.rect.right = screen_width
            self.speed.x *= -1
        if self.rect.top < 0:
            self.rect.top = 0
            self.speed.y *= -1
        elif self.rect.bottom > screen_height:
            self.rect.bottom = screen_height
            self.speed.y *= -1
    
    def draw(self, surface):
        # 绘制鱼
        surface.blit(self.img, self.rect)

# 创建大鱼和小鱼
big_fish = Fish(Vector2(screen_width/2, screen_height/2), img_fish_big)
small_fish_list = []
for i in range(10):
    x = pygame.math.Vector2(pygame.math.randint(0, screen_width), pygame.math.randint(0, screen_height))
    small_fish_list.append(Fish(x, img_fish_small))

# 游戏循环
running = True
while running:
    # 处理事件
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    
    # 检测大鱼和小鱼是否碰撞
    for small_fish in small_fish_list:
        distance = big_fish.rect.center - small_fish.rect.center
        if distance.length() < 50:
            # 大鱼吃掉小鱼
            img_fish_big = pygame.transform.rotozoom(img_fish_big, 0, 1.1)
            small_fish_list.remove(small_fish)
    
    # 更新大鱼和小鱼
    big_fish.update()
    for small_fish in small_fish_list:
        small_fish.update()
    
    # 绘制画面
    screen.fill((255, 255, 255))
    big_fish.draw(screen)
    for small_fish in small_fish_list:
        small_fish.draw(screen)
    pygame.display.update()

# 退出pygame
pygame.quit()

这个代码中，我们创建了一个 `Fish` 类来表示鱼，其中包含了位置、图片、速度等属性，以及更新位置、绘制鱼等方法。

在游戏循环中，我们先检测大鱼和小鱼是否碰撞，如果距离小于50像素，则大鱼吃掉小鱼，并将大鱼图片放大。然后更新大鱼和小鱼的位置，并绘制画面。

注意，为了让程序更加健壮，我们对鱼的位置进行了限制，保证鱼不会飞出屏幕。同时，我们使用了 `pygame.math` 中的 `Vector2` 类来方便地计算距离和速度。