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  • python中 try、except、finally 的执行顺序

     
     
    def test1():
    try:
    print('to do stuff')
    raise Exception('hehe')
    print('to return in try')
    return 'try'
    except Exception:
    print('process except')
    print('to return in except')
    return 'except'
    finally:
    print('to return in finally')
    return 'finally'

    test1Return = test1()
    print('test1Return : ' + test1Return)

    输出:

    to do stuff
    process except
    to return in except
    to return in finally
    test1Return : finally

     
    在 try 中 raise一个异常,就立刻转入 except 中执行,在except 中遇到 return 时,就强制转到 finally 中执行, 在 finally 中遇到 return 时就返回
     
    def test2():
    try:
    print('to do stuff')
    print('to return in try')
    return 'try'
    except Exception:
    print('process except')
    print('to return in except')
    return 'except'
    finally:
    print('to return in finally')
    return 'finally'

    test2Return = test2()
    print('test1Return : ' + test2Return)
    输出:

    to do stuff
    to return in try
    to return in finally
    test2Return : finally

    这里在 try 中没有抛出异常,因此不会转到 except 中,但是在try 中遇到return时,也会立即强制转到finally中执行,并在finally中返回

    test1和test2得到的结论:

    无论是在try还是在except中,遇到return时,只要设定了finally语句,就会中断当前的return语句,跳转到finally中执行,如果finally中遇到return语句,就直接返回,不再跳转回try/excpet中被中断的return语句

    def test3():
    i = 0
    try:
    i += 1
    print('i in try : %s'%i)
    raise Exception('hehe')
    except Exception:
    i += 1
    print('i in except : %s'%i)
    return i
    finally:
    i += 1
    print ('i in finally : %s'%i )

    print('test3Return : %s'% test3())

    输出:

    i in try : 1
    i in except : 2
    i in finally : 3
    test3Return : 2

    def test4():
    i = 0
    try:
    i += 1
    return i
    finally:
    i += 1
    print ('i in finally : %s'%i )
    print('test4Return : %s' % test4())
    输出

    i in finally : 2
    test4Return : 1

    test3和test4得到的结论:

    在except和try中遇到return时,会锁定return的值,然后跳转到finally中,如果finally中没有return语句,则finally执行完毕之后仍返回原return点,将之前锁定的值返回(即finally中的动作不影响返回值),如果finally中有return语句,则执行finally中的return语句。

    def test5():
    for i in range(5):
    try:
    print('do stuff %s'%i)
    raise Exception(i)
    except Exception:
    print('exception %s'%i)
    continue
    finally:
    print('do finally %s'%i)
    test5()

    输出

    do stuff 0
    exception 0
    do finally 0
    do stuff 1
    exception 1
    do finally 1
    do stuff 2
    exception 2
    do finally 2
    do stuff 3
    exception 3
    do finally 3
    do stuff 4
    exception 4
    do finally 4

    test5得到的结论:

    在一个循环中,最终要跳出循环之前,会先转到finally执行,执行完毕之后才开始下一轮循环

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  • 原文地址:https://www.cnblogs.com/ybwang/p/4738621.html
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