详解在Python程序中自定义异常的方法

脚本专栏 2024/11/25 佚名

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通过创建一个新的异常类，程序可以命名它们自己的异常。异常应该是典型的继承自Exception类，通过直接或间接的方式。
以下为与RuntimeError相关的实例,实例中创建了一个类，基类为RuntimeError，用于在异常触发时输出更多的信息。
在try语句块中，用户自定义的异常后执行except块语句，变量 e 是用于创建Networkerror类的实例。

class Networkerror(RuntimeError):
  def __init__(self, arg):
   self.args = arg

在你定义以上类后，你可以触发该异常，如下所示：

try:
  raise Networkerror("Bad hostname")
except Networkerror,e:
  print e.args

在下面这个例子中，默认的__init__()异常已被我们重写。

> 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 "<stdin>", line 1, in "htmlcode">

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

Python,自定义异常