Python 学习笔记18 异常处理

我们在编码的过程中,难免会遇到一些错误和异常, 这时候程序会异常退出,并且会抛出错误信息:

比如:

 

print(1/0)

'''
输出:
Traceback (most recent call last):
  File "D:/PythonStudy/errors.py", line 3, in <module>
    print(1/0)
ZeroDivisionError: division by zero
'''

 

我们尝试让1 去除0,结果系统报错了异常  ‘ZeroDivisionError: division by zero’, 表示不能被零除。

Python内置许多异常,当出现这些问题时,会提示我们并中断运行,python3.7中主要有以下的异常:

BaseException
 +-- SystemExit
 +-- KeyboardInterrupt
 +-- GeneratorExit
 +-- Exception
      +-- StopIteration
      +-- StopAsyncIteration
      +-- ArithmeticError
      |    +-- FloatingPointError
      |    +-- OverflowError
      |    +-- ZeroDivisionError
      +-- AssertionError
      +-- AttributeError
      +-- BufferError
      +-- EOFError
      +-- ImportError
      |    +-- ModuleNotFoundError
      +-- LookupError
      |    +-- IndexError
      |    +-- KeyError
      +-- MemoryError
      +-- NameError
      |    +-- UnboundLocalError
      +-- OSError
      |    +-- BlockingIOError
      |    +-- ChildProcessError
      |    +-- ConnectionError
      |    |    +-- BrokenPipeError
      |    |    +-- ConnectionAbortedError
      |    |    +-- ConnectionRefusedError
      |    |    +-- ConnectionResetError
      |    +-- FileExistsError
      |    +-- FileNotFoundError
      |    +-- InterruptedError
      |    +-- IsADirectoryError
      |    +-- NotADirectoryError
      |    +-- PermissionError
      |    +-- ProcessLookupError
      |    +-- TimeoutError
      +-- ReferenceError
      +-- RuntimeError
      |    +-- NotImplementedError
      |    +-- RecursionError
      +-- SyntaxError
      |    +-- IndentationError
      |         +-- TabError
      +-- SystemError
      +-- TypeError
      +-- ValueError
      |    +-- UnicodeError
      |         +-- UnicodeDecodeError
      |         +-- UnicodeEncodeError
      |         +-- UnicodeTranslateError
      +-- Warning
           +-- DeprecationWarning
           +-- PendingDeprecationWarning
           +-- RuntimeWarning
           +-- SyntaxWarning
           +-- UserWarning
           +-- FutureWarning
           +-- ImportWarning
           +-- UnicodeWarning
           +-- BytesWarning
           +-- ResourceWarning

 有关内置异常的详细描述可以参考python的相关文档,链接如下: https://docs.python.org/zh-cn/3/library/exceptions.html#bltin-exceptions

 

Python提供了一套方式,用来捕获和处理错误和异常:

使用try....except...finally来对可能存在的错误进行处理:

#-*- coding:utf-8 -*-

try:
    print(1/0)
except ZeroDivisionError:
    print('Can not division 0, happen ZeroDivisionError')
finally:
    print('Go to next step')

'''
输出:
Can not division 0, happen ZeroDivisionError
Go to next step
'''

 

通过上面的例子,我们可以看到,代码首先执行try里的code,如果遇到了指定的错误,那么就执行except中的代码, 处理完毕后执行finally中的代码。

在每个代码块中,支持各种判断和迭代,其工作的流程结构如下:

 

 除了系统内置的错误,我们也可以在代码中主动抛出一些错误:

#-*- coding:utf-8 -*-
name = 'ralf'
if name != 'rachel':
    raise Exception('The name is not ralf')

'''
输出:
Traceback (most recent call last):
  File "D:/PythonStudy/errors.py", line 4, in <module>
    raise Exception('The name is not ralf')
Exception: The name is not ralf
'''

 

我们也可以通过继承Exception base class,自定我们自己的错误类型:

#-*- coding:utf-8 -*-
class NameError(Exception):
    def __init__(self, level, message):
        self.level = level
        self.message = message
try:
    name = 'ralf'
    if name != 'rachel':
        raise NameError('Error', 'Name is not right')
except NameError as e:
    print(e.level)
    print(e.message)
'''
输出:
Error
Name is not right
'''

 

posted @ 2019-07-21 17:07  追风狂想  阅读(312)  评论(0编辑  收藏  举报