这是我个人认为最简单的解决方案，用于定义带有默认消息的自定义异常，如果需要可以覆盖：
class CustomException(Exception):
def __init__(self, msg='My default message', *args, **kwargs):
super().__init__(msg, *args, **kwargs)
使用示例：
In [10]: raise CustomException
---------------------------------------------------------------------------
CustomException Traceback (most recent call last)
<ipython-input-10-259ae5202c8e> in <module>
----> 1 raise CustomException
CustomException: My default message
In [11]: raise CustomException()
---------------------------------------------------------------------------
CustomException Traceback (most recent call last)
<ipython-input-11-c1921a8781a6> in <module>
----> 1 raise CustomException()
CustomException: My default message
In [12]: raise CustomException('Foo bar')
---------------------------------------------------------------------------
CustomException Traceback (most recent call last)
<ipython-input-12-7efbf94f7432> in <module>
----> 1 raise CustomException('Foo bar')
CustomException: Foo bar
解决方案如下所示：
class CustomException(Exception):
def __init__(self, *args, **kwargs):
default_message = 'This is a default message!'
# if any arguments are passed...
# If you inherit from the exception that takes message as a keyword
# maybe you will need to check kwargs here
if args:
# ... pass them to the super constructor
super().__init__(*args, **kwargs)
else: # else, the exception was raised without arguments ...
# ... pass the default message to the super constructor
super().__init__(default_message, **kwargs)
一个等效但更简洁的解决方案是：
class CustomException(Exception):
def __init__(self, *args, **kwargs):
default_message = 'This is a default message!'
# if no arguments are passed set the first positional argument
# to be the default message. To do that, we have to replace the
# 'args' tuple with another one, that will only contain the message.
# (we cannot do an assignment since tuples are immutable)
# If you inherit from the exception that takes message as a keyword
# maybe you will need to check kwargs here
if not args: args = (default_message,)
# Call super constructor
super().__init__(*args, **kwargs)
更加简洁但限制较多的解决方案是，您只能使用无参数的方式触发CustomException：
以下是实现代码:
class CustomException(Exception):
def __init__(self):
default_message = 'This is a default message!'
super().__init__(default_message)
如果您只是将字符串文字传递给构造函数而不使用default_message变量，则可以在上述每个解决方案中节省一行。
如果您想使代码与Python 2.7兼容，则只需用super(CustomException, self)替换super()。
现在运行：
>>> raise CustomException
将输出：
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.CustomException: This is a default message!
并运行：
raise CustomException('This is a custom message!')
将输出:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.CustomException: This is a custom message!
这是前两个解决方案的代码将产生的输出。最后一个解决方案不同之处在于，如果至少使用一个参数调用它，如：
raise CustomException('This is a custom message!')
它将输出：
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: __init__() takes 1 positional argument but 2 were given
因为它不允许在引发CustomException时传递任何参数。
在回答这个问题时，以下是一种声明自定义异常的相当不错的方式：
class MyException(Exception):
"""Docstring here"""
如果需要定义许多异常，可以使用Exception类的子类作为这些异常的超类，使得这些异常的文档字符串成为它们的默认信息：
class DocDefaultException(Exception):
"""Subclass exceptions use docstring as default message"""
def __init__(self, msg=None, *args, **kwargs):
super().__init__(msg or self.__doc__, *args, **kwargs)
class MyException(DocDefaultException):
"""Docstring here."""
raise MyException
输出：
Traceback (most recent call last):
File "C:\************************.py", line 9, in <module>
raise MyException
__main__.MyException: Docstring here
import functools
def docstring_message(cls):
"""Decorates an exception to make its docstring its default message."""
# Must use cls_init name, not cls.__init__ itself, in closure to avoid recursion
cls_init = cls.__init__
@functools.wraps(cls.__init__)
def wrapped_init(self, msg=cls.__doc__, *args, **kwargs):
cls_init(self, msg, *args, **kwargs)
cls.__init__ = wrapped_init
return cls
@docstring_message
class MyException(Exception):
"""Docstring here"""
raise MyException
输出：
Traceback (most recent call last):
File "C:\************************.py", line 16, in <module>
raise MyException
__main__.MyException: Docstring here
class PinNotFoundError(BaseException):
""" Error class to thrown, when a pin cannot be found """
def __init__(self, pin, *args, **kwargs):
msg = f'Pin {pin} cannot be resolved to a pin on the device.'
super().__init__(msg, *args, **kwargs)
class DefaultException(Exception):
"""A class to define a default message with the exception definition"""
MSG = ''
def __init__(self, *args, message=None, **kwargs):
if message is None:
message = self.MSG
super().__init__(message)
class CustomException(DefaultException):
"""This is just an example exception"""
MSG = 'This is a default message!'
DefaultException，使用kwargs来格式化默认消息，如果你也想要一些格式化。