Python中自定义异常的使用举例

class Networkerror(RuntimeError):

  def __init__(self, arg):

   self.args = arg

try:

  raise Networkerror("Bad hostname")

except Networkerror,e:

  print e.args

>>> 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 ?

__main__.MyError: 'oops!'

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