Exception

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try..exception的写法如下所示，当文件不存在的时候出现error，输入错误信息

当文件存在时，执行else语句，关闭文件。不管OK还是NG都会执行finally语句。

import sys  try:  f = open("mfile.txt")  except IOError as e:  print("NO mfile.txt")  print("system error message is :{0}".format(e))  else:  print("close mfile")  f.close()finally:print("finally")

Exception有个特殊tuple属性args用来存储参数，同样默认的__str__也是用的参数，所以在有参数并且没有定义__str__的Exception中，直接打印对象和args是相同的。

try:raise Exception('spam', 'eggs')except Exception as e:print(type(e))print(e.args)print(e)#输出结果为<class 'Exception'>('spam', 'eggs')('spam', 'eggs')

自定义Exception

class MyError(Exception):def __init__(self, myarg):self.myarg = myargdef __str__(self):return self.myargif __name__ == "__main__":try:raise MyError("my error")except MyError as e:print(e.args)print(e)# 输出结果# ('my error',)# my error

Python的内置异常类的继承关系如下所示

BaseException +-- SystemExit +-- KeyboardInterrupt +-- GeneratorExit +-- Exception      +-- StopIteration      +-- ArithmeticError      |    +-- FloatingPointError      |    +-- OverflowError      |    +-- ZeroDivisionError      +-- AssertionError      +-- AttributeError      +-- BufferError      +-- EOFError      +-- ImportError      +-- 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      +-- SyntaxError      |    +-- IndentationError      |         +-- TabError      +-- SystemError      +-- TypeError      +-- ValueError      |    +-- UnicodeError      |         +-- UnicodeDecodeError      |         +-- UnicodeEncodeError      |         +-- UnicodeTranslateError      +-- Warning           +-- DeprecationWarning           +-- PendingDeprecationWarning           +-- RuntimeWarning           +-- SyntaxWarning           +-- UserWarning           +-- FutureWarning           +-- ImportWarning           +-- UnicodeWarning           +-- BytesWarning           +-- ResourceWarning

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