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CS50P: 3. Exceptions

SyntaxError

语法错误

ValueError

情况一：user输入非期望数据类型

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x = int(input("What's x? "))
print(f"x is {x}")

如果用户输入 cat ，会得到 ValueError: invalid literal for int() with base 10: 'catcat'

解决方案：

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try:
    x = int(input("What's x? "))
    print(f"x is {x}")
except ValueError:
    print("x is not an interger")

try & except

python关键字

NameError

doing sth with a variable that u shouldn't

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try:
    x = int(input("What's x? "))
except ValueError:
    print("x is not an interger")
print(f"x is {x}")

如果输入 wolffy ，返回 x is not an interger 和 NameError: name 'x' is not defined ，因为在 int 接收字符串输入的时候就已经发生了ValueError，右边的值并未赋给左边。

赋值即定义？

增加else

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try:
    x = int(input("What's x? "))
except ValueError:
    print("x is not an interger")
else:
    print(f"x is {x}")

如果try成功了，没出现Error，就会执行 print(x)；如果try失败，执行except来处理ValueError，然后跳出程序(当前代码块，跳到下一个阶段)

改进

直到user输入合法才停止

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while True:
    try:
        x = int(input("What's x? "))
    except ValueError:
        print("x is not an interger")
    else:
        break
print(f"x is {x}")

pass

跳过某种情况，catch it, and ignore it

例如：

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except ValueError:
    pass

Pythonic: try things, hopefully they work, but if they don't, handle the exception

不同于C的使用if

raise