Python----面向对象---try....except的详细用法

try..except...详细用法

1、如果一段代码有多种类型的错误，例如:

try:
    print('======1')
    name
    print('======2')
    l = [1, 2, 3]
    l[100]
    print('======3')
    d = {}
    d['name']
    print('======4')

except NameError as e:
    print('---->', e)

结果为：

======1
----> name 'name' is not defined

定制什么类型异常，能捕获相应的异常，但是没有指定的异常的话还是会报错的，

try:
    print('======1')
    # name
    print('======2')
    l = [1, 2, 3]
    l[100]
    print('======3')
    d = {}
    d['name']
    print('======4')

except NameError as e:
    print('---->', e)

结果为：

======1
Traceback (most recent call last):
======2
  File "C:/Users/xu516/PycharmProjects/Python全栈开发/第三模块/面向对象编程/33 try...except详细用法.py", line 8, in <module>
    l[100]
IndexError: list index out of range

这样的话，能不能写多个except呢，答案是可以的，这就是异常的多分支

try:
    print('======1')
    # name
    print('======2')
    l = [1, 2, 3]
    # l[100]
    print('======3')
    d = {}
    d['name']
    print('======4')

except NameError as e:
    print('---->', e)

except IndexError as e:
    print('---->', e)

except KeyError as e:
    print('---->', e)

结果为：

======1
======2
======3
----> 'name'

这样就能捕获多种类型的异常，

多分支：被检测的代码块抛出的异常有多种可能性，并且我们需要针对每一种异常类型都定制专门的处理逻辑

try:
    print('======1')
    # name
    print('======2')
    l = [1, 2, 3]
    # l[100]
    print('======3')
    d = {}
    d['name']
    print('======4')

except NameError as e:
    print('---->', e)

except IndexError as e:
    print('---->', e)

except KeyError as e:
    print('---->', e)

print('after code')

结果为：

======1
======2
======3
----> 'name'
after code

捕获异常后的代码会正常执行，

万能异常：Exception ,被检测的代码块抛出的异常有多种可能性，并且我们针对所有的异常类型都只用一种处理逻辑就可以了，那就使用Exception，

try:
    print('======1')
    # name
    print('======2')
    l = [1, 2, 3]
    # l[100]
    print('======3')
    d = {}
    d['name']
    print('======4')

except Exception as e:
    print('---->', e)


print('after code')

结果为:

 ======1
======2
======3
----> 'name'
after code

当然，万能异常也可以和定制异常混合使用，除了我们关心的异常使用定制异常，其它的异常类型我们使用万能异常

代码示例如下：

try:
    print('======1')
    name
    print('======2')
    l = [1, 2, 3]
    l[100]
    print('======3')
    d = {}
    d['name']
    print('======4')

except NameError as e:
    print('---->', e)

except IndexError as e:
    print('---->', e)

except KeyError as e:
    print('---->', e)

except Exception as e:
    print('---->', e)


print('after code')

结果为：

======1
----> name 'name' is not defined
after code

 还可以在except后加else判断语句，该语句会在被检测的代码块没有发生异常时执行

如：

try:
    print('======1')
    # name
    print('======2')
    l = [1, 2, 3]
    # l[100]
    print('======3')
    d = {}
    # d['name']
    print('======4')

except NameError as e:
    print('---->', e)

except IndexError as e:
    print('---->', e)

except KeyError as e:
    print('---->', e)

except Exception as e:
    print('---->', e)

else:
    print('在被检测代码块没有发生异常时执行')


print('after code')

结果为：

======1
======2
======3
======4
在被检测代码块没有发生异常时执行
after code

加finally语句，不管被检测的代码块有没有发生异常都会执行

try:
    print('======1')
    # name
    print('======2')
    l = [1, 2, 3]
    # l[100]
    print('======3')
    d = {}
    d['name']
    print('======4')

except NameError as e:
    print('---->', e)

except IndexError as e:
    print('---->', e)

except KeyError as e:
    print('---->', e)

except Exception as e:
    print('---->', e)

else:
    print('在被检测代码块没有发生异常时执行')

finally:
    print('不管被检测的代码块有没有发生异常都会执行')


print('after code')

结果为：


======1
======2
======3
----> 'name'
不管被检测的代码块有没有发生异常都会执行
after code

finally的代码应用案例：

try:
    f = open('a.txt')
    print(next(f))
    print(next(f))
    print(next(f))
    print(next(f))
    print(next(f))
    print(next(f))
    print(next(f))

finally:
    print('final')
    f.close()

结果为：

111
Traceback (most recent call last):

222

333
  File "C:/Users/xu516/PycharmProjects/Python全栈开发/第三模块/面向对象编程/33 try...except详细用法.py", line 42, in <module>

444
    print(next(f))

StopIteration
555
final