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                合規國際互聯網加速 OSASE為企業客戶提供高速穩定SD-WAN國際加速解決方案。 廣告
                在程序中可以通過創建新的異常類型來命名自己的異常(Python 類的內容請參見?[_類_](http://www.pythondoc.com/pythontutorial3/classes.html#tut-classes)?)。異常類通常應該直接或間接的從?Exception?類派生,例如: ~~~ >>> class MyError(Exception): ... def __init__(self, value): ... self.value = value ... def __str__(self): ... return repr(self.value) ... >>> try: ... raise MyError(2*2) ... except MyError as e: ... print('My exception occurred, value:', e.value) ... My exception occurred, value: 4 >>> raise MyError('oops!') Traceback (most recent call last): File "", line 1, in ? __main__.MyError: 'oops!' ~~~ 在這個例子中,Exception?默認的?__init__()?被覆蓋。新的方式簡單的創建?_value_?屬性。這就替換了原來創建?_args_?屬性的方式。 異常類中可以定義任何其它類中可以定義的東西,但是通常為了保持簡單,只在其中加入幾個屬性信息,以供異常處理句柄提取。如果一個新創建的模塊中需要拋出幾種不同的錯誤時,一個通常的作法是為該模塊定義一個異常基類,然后針對不同的錯誤類型派生出對應的異常子類: ~~~ class Error(Exception): """Base class for exceptions in this module.""" pass class InputError(Error): """Exception raised for errors in the input. Attributes: expression -- input expression in which the error occurred message -- explanation of the error """ def __init__(self, expression, message): self.expression = expression self.message = message class TransitionError(Error): """Raised when an operation attempts a state transition that's not allowed. Attributes: previous -- state at beginning of transition next -- attempted new state message -- explanation of why the specific transition is not allowed """ def __init__(self, previous, next, message): self.previous = previous self.next = next self.message = message ~~~ 與標準異常相似,大多數異常的命名都以 “Error” 結尾。 很多標準模塊中都定義了自己的異常,用以報告在他們所定義的函數中可能發生的錯誤。關于類的進一步信息請參見?[_類_](http://www.pythondoc.com/pythontutorial3/classes.html#tut-classes)?一章。
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