Python学习VII --- 异常处理_python 引发异常 raise()及异常处理

本文介绍了Python中的异常处理机制，包括try...except...等结构的使用方法，并演示了如何通过raise重新抛出异常。此外，还提供了自定义异常类的示例。

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这篇博客主要是阅读python之旅时做的笔记。提取出最主要的知识点，供个人在以后中快速查阅。

常见组合

try...except...
try...except...else...
try...except...else...finally...
try...except...except...else...finally...
try...finally...

try:
    x = input('Enter x: ')
    y = input('Enter y: ')
    print x / y
except ZeroDivisionError as e:
    print 'ZeroDivisionError:',e
except TypeError as e:
    print 'TypeError:',e
except BaseException as e:    # 捕获其他异常
    print 'BaseException:',e
else:                 # 当没有异常时，执行else
    print 'no error!'

因为BaseException是所有异常的父类。

Finally

try:
    x = 1/0
    print x
finally:            # 不管三七二十一，这个都要执行
    print 'DONE'

raise异常

有时候捕获了异常，还想再把异常抛出去。

try:
    x = input('Enter x: ')
    y = input('Enter y: ')
    print x / y
except ZeroDivisionError as e:
    print 'ZeroDivisionError:',e
except TypeError as e:
    print 'TypeError:',e
except BaseException as e:
    print 'BaseException:',e
    raise                           # 使用 raise 抛出异常，不用带参数
else:
    print 'no error!'

print 'hello world'

Exception类 — 自定义异常类

# 自定义异常类
class SomeError(Exception):
    pass

try:
    x = input('Enter x: ')
    y = input('Enter y: ')
    print x / y
except ZeroDivisionError as e:
    print 'ZeroDivisionError:',e
except TypeError as e:
    print 'TypeError:',e
except BaseException as e:
    print 'BaseException:',e
    raise SomeError('invalid value')    # 抛出自定义的异常
else:
    print 'no error!'

print 'hello world'


Enter x: 
BaseException: unexpected EOF while parsing (<string>, line 0)
----------------------------------------------------------------------
SomeError                            Traceback (most recent call last)
<ipython-input-20-66060b472f91> in <module>()
     12 except BaseException as e:
     13     print 'BaseException:',e
---> 14     raise SomeError('invalid value')
     15 else:
     16     print 'no error!'

SomeError: invalid value