异常处理

2024-06-06
2025-04-27
  1"""
  2Author: wangy325
  3Date: 2024-07-16 21:07:13
  4Description: 异常的处理和抛出, else语句, finally语句, 异常组
  5"""
  6
  7
  8class B(Exception):
  9    pass
 10
 11
 12class C(B):
 13    pass
 14
 15
 16class D(C):
 17    pass
 18
 19
 20for els in [B, C, D]:
 21    try:
 22        raise els
 23    except D:
 24        print('D')
 25    except C:
 26        print('C')
 27    except B:
 28        print('B')
 29'''
 30展示了异常的传递和匹配:
 31抛出的异常是exception捕获异常的子类可以匹配上, 反之不行
 32这很好理解啊
 33`raise`语句相当于主动抛出异常
 34`else`子句只有在try语句没有发生异常时才执行.
 35所以, `else`语句可以避免意外捕获一些非try块引发的异常.
 36'''
 37a, b = 1, '2'
 38try:
 39    c = a + b
 40except TypeError as e:
 41    print(f'{e.__class__}: {e} ')
 42else:
 43    print(f'else block: {c}')
 44
 45# But, how about a exception occurs in else sub-sentence?
 46# Solution 1: use extra try...exception to handle that.
 47# Solution 2: use finally sub-sentence to re-raise exception.
 48# Best way is, make sure your else sub-sentence clean.
 49try:
 50    print('try ok!')
 51except SystemError:
 52    print('never mind')
 53else:
 54    try:
 55        2 / 0
 56    except ZeroDivisionError as e:
 57        print(f'else error: {e}')
 58
 59
 60def how_finally_works(x, y):
 61    try:
 62        return x / y
 63    except ZeroDivisionError as exp:
 64        print(f"{exp}: can not divide by 0")
 65        return 0
 66    finally:
 67        print('finally...')
 68        return -1
 69
 70
 71# 返回finally子句的值
 72print(how_finally_works(2, 3), end='\n---------\n')
 73print(how_finally_works(2, 0), end='\n---------\n')
 74print(how_finally_works('a', 'b'), end='\n---------\n')
 75'''
 761) finally 子句一定会执行(调用1,2,3)
 772) finally 子句的返回值会覆盖try块的返回值(调用2)
 783) finally 子句有return语句, 会覆盖未处理的异常(调用3)
 79
 80他么的, 究竟是谁会在finally块中写返回值啊
 81'''
 82
 83
 84def how_finally_works2():
 85    try:
 86        slt = []
 87        for i in reversed(range(-1, 3)):
 88            if i < 0:
 89                break
 90            slt.append(10 / i)
 91        # return slt
 92    except ZeroDivisionError as e:
 93        print(f'{e.__class__}: {e}')
 94    else:
 95        print('else here.')
 96        return slt
 97    finally:
 98        print('finally here.')
 99
100
101print(how_finally_works2())
102'''
1031. 如果try子句中存在return语句, 且没有发生异常, 则else子句不再执行.
1042. 如果try子句中存在return语句, 发生异常且被捕获, finally语句在return之前执行
105'''
106
107print('-----ExceptionGroup-----')
108
109
110def f():
111    es = [OSError('error 1'), SystemError('error 2')]
112    raise ExceptionGroup('there are problems: ', es)
113
114
115f()
116'''
117ExceptionGroup 是3.11之后引进的新特性
118'''
xf&pl

异常处理
