291 lines
5.2 KiB
Markdown
291 lines
5.2 KiB
Markdown
# 流程控制
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## 判断语句(if)
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**语法：**
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```python
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if 条件:
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满足条件后要执行的代码
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```
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<img src="./01.python流程控制/image-20240904142740373.png" alt="image-20240904142740373" style="zoom:80%;" />
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### 单分支判断
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```python
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# 提示用户输入年龄
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age = int(input("请输入你的年龄："))
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# 单分支判断
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if age >= 18:
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print("已经成年，可以去网吧上网了")
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print("欢迎来到Eagles网吧")
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print("你还没成年，要好好学习")
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```
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### 双分支判断
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```python
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"""
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if 条件:
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满足条件执行代码
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else:
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if条件不满足就走这段
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"""
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# 提示用户输入年龄
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age = int(input("请输入你的年龄："))
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# 单分支判断
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if age >= 18:
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print("已经成年，可以去网吧上网了")
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print("欢迎来到Eagles网吧")
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else:
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print("你还没成年，要好好学习")
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```
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### 多分支判断
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```python
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if 条件:
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满足条件执行代码
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elif 条件:
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上面的条件不满足就走这个
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elif 条件:
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上面的条件不满足就走这个
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elif 条件:
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上面的条件不满足就走这个
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else:
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上面所有的条件不满足就走这段
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# 成绩判断程序
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# 提示用户输入成绩
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score = int(input("请输入成绩（0-100）："))
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# 多分支判断成绩
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if score >= 90 and score <= 100:
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print("优秀")
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elif score >= 60 and score < 90:
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print("良好")
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elif score >= 0 and score < 60:
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print("不及格")
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else:
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print("输入错误，请输入0到100之间的成绩。")
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```
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## 循环语句-while
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**语法：**
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```python
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while 条件:
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循环体
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# 循环条件可以直接是True/False或者1/0，也可以是某个语句...
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```
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如果条件为真，那么循环体则执行
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如果条件为假，那么循环体不执行
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**示例：猜数字小游戏**
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```python
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print('猜数字游戏开始')
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num = 54
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while True:
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guess = int(input("您猜数字是什么？(输入0-100的数字):"))
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if guess < num:
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print("您猜小了")
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continue
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elif guess > num:
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print("您猜大了")
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continue
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break
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print("您猜对了！")
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# Output:
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猜数字游戏开始
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您猜数字是什么？(输入0-100的数字):10
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您猜小了
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您猜数字是什么？(输入0-100的数字):50
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您猜小了
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您猜数字是什么？(输入0-100的数字):60
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您猜大了
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您猜数字是什么？(输入0-100的数字):54
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您猜对了！
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```
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### 循环终止语句
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#### break
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用于完全结束一个循环，跳出循环体执行循环后面的语句
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#### continue
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和 break 有点类似，区别在于 continue 只是终止本次循环，接着还执行后面的循环，break 则完全终止循环
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#### while...else结构
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while 后面的 else 作用是指，当 while 循环正常执行完，中间没有被 break 中止的话，就会执行 else 后面的语句
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- **语法：**
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```python
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while condition:
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# 循环体
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if some_condition:
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break
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else:
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# 循环正常结束时执行的代码
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```
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- **示例：**
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```python
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# 寻找素数的示例
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num = 10
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i = 2
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while i < num:
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if num % i == 0:
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print(f"{num} 不是素数，因为它可以被 {i} 整除。")
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break
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i += 1
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else:
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print(f"{num} 是一个素数！")
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```
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## 循环语句-for
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for循环：用户按照顺序循环可迭代对象的内容
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**语法：**
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```python
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for variable in iterable:
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# 循环体
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# 执行的代码
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```
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### 遍历列表
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```python
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fruits = ["apple", "banana", "cherry"]
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for fruit in fruits:
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print(fruit)
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# Output:
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apple
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banana
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cherry
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```
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### 遍历字符串
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```python
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word = "helloworld"
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for letter in word:
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print(letter)
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# Output:
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h
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e
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l
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l
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o
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w
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o
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r
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l
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d
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```
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## enumerate
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enumerate：枚举，对于一个可迭代的（iterable）/可遍历的对象（如列表、字符串），enumerate将其组成一个索引序列，利用它可以同时获得索引和值。
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```python
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li = ['甲','乙','丙','丁']
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for i in enumerate(li):
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print(i)
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for index,value in enumerate(li):
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print(index,value)
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for index,value in enumerate(li,100): #从哪个数字开始索引
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print(index,value)
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# Output:
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(0, '甲')
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(1, '乙')
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(2, '丙')
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(3, '丁')
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0 甲
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1 乙
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2 丙
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3 丁
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100 甲
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101 乙
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102 丙
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103 丁
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```
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## range
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指定范围，生成指定数字
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```bash
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for i in range(1,10):
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print(i)
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for i in range(1,10,2): # 步长
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print(i)
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for i in range(10,1,-2): # 反向步长
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print(i)
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```
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### 小游戏案例
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石头简单布
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```bash
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import random
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# random产生随机值或者从给定值中随机选择
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# 可选择的选项
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options = ["石头", "剪子", "布"]
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print("欢迎来到石头剪子布游戏！")
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print("请从以下选项中选择：")
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for i, option in enumerate(options):
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print(f"{i + 1}. {option}")
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# 玩家选择
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player_choice = int(input("请输入你的选择（1-3）：")) - 1
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# 计算机随机选择
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computer_choice = random.randint(0, 2)
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print(f"\n你选择了：{options[player_choice]}")
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print(f"计算机选择了：{options[computer_choice]}")
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# 判断胜负
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if player_choice == computer_choice:
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print("平局！")
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elif (player_choice == 0 and computer_choice == 1) or \
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(player_choice == 1 and computer_choice == 2) or \
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(player_choice == 2 and computer_choice == 0):
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print("你赢了！🎉")
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else:
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print("你输了！😢")
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```
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