1、什么是异常

异常通常是指因各种原因的出错程序代码不能正常运行，从而返回报错信息，中断程序。

报错信息由两部分组成（1）Traceback：追溯出错的源头（2）异常所属的类，以及提示的上下文。

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#Traceback (most recent call last):
# File "<stdin>", line 1, in <module>
# ZeroDivisionError: division by zero

#如上：异常属于ZeroDivisionError，并使用默认的上下文提示division by zero
  • 常见的异常类都属于Exception这个父类，而具体的一些异常类型由它继承而来，一般为****Error
image-20220408075342628

2、捕捉异常

  • 出现异常，程序会立即中断执行。

  • 如果只是想捕捉并提醒到某个预知的异常，而不影响后续代码的运行，可以使用下面的方法。

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##(1) 预知会出现指定类型的错误，并使用默认的上下文提示异常信息
try:
    x = 1
    y = 0
    print(x/y)
except ZeroDivisionError as e:
    print(e)
# division by zero

##(2) 预知会出现指定类型的错误，并自定义提示信息
try:
    x = 1
    y = 0
    print(x/y)
except ZeroDivisionError:
    print("The second number cannot be zero!")
# The second number cannot be zero!
  • 当不确定会出现某种预知的类别时
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##(1) 使用多个except语句
try:
    x = 1
    y = "aaaa"
    print(x/y)
except ValueError as e:
    print(e)
except ZeroDivisionError as e:
    print(e)
except TypeError as e:
    print(e)
# unsupported operand type(s) for /: 'int' and 'str'

##(2) 使用元组囊括多种异常类别
try:
    x = 1
    y = "aaaa"
    print(x/y)
except (ValueError, ZeroDivisionError, TypeError) as e:
    print(e)
# unsupported operand type(s) for /: 'int' and 'str'

##(3) 仅使用except语句，直接捕捉所有异常事件
try:
    x = 1
    y = 0
    print(x/y)
except:
    print("Something wrong happened！")
# Something wrong happened！

3、搭配其它语句

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##(1) raise语句：触发指定类型错误，中断程序执行
def calc(number1, number2, muffled=False):
    'muffled参数设置为：是否捕捉异常'
    try:
        print(number1/number2)
    except ZeroDivisionError:
        if muffled:
            print("The second number cannot be zero! But you can go on")
        else:
            raise ZeroDivisionError("The second number cannot be zero! You are stopped")

calc(1,0, muffled=True)
#The second number cannot be zero! But you can go on
calc(1,0, muffled=False)
# Traceback (most recent call last):
#  File "<stdin>", line 1, in <module>
#  File "<stdin>", line 9, in calc
# ZeroDivisionError: The second number cannot be zero! You are stopped


##(2) else语句：类似if-else语句，如果没报错....
try:
    x = 10
    y = 1
    z = x/y
except Exception as e:
    print(e)
else:
    print("The number you provied is good. And the result is", z)
# The number you provied is good. And the result is 10.0