BaseException.message deprecated in Python 2.6

Question

I get a warning that BaseException.message is deprecated in Python 2.6 when I use the following user-defined exception:

class MyException(Exception):

def __init__(self, message):
    self.message = message

def __str__(self):
    return repr(self.message)

This is the warning:

DeprecationWarning: BaseException.message has been deprecated as of Python 2.6 self.message = message

What's wrong with this? What do I have to change to get rid of the deprecation warning?

Answer 1

Yes, it's deprecated in Python 2.6 because it's going away in Python 3.0

BaseException class does not provide a way to store error message anymore. You'll have to implement it yourself. You can do this with a subclass that uses a property for storing the message.

class MyException(Exception):
    def _get_message(self): 
        return self._message
    def _set_message(self, message): 
        self._message = message
    message = property(_get_message, _set_message)

Hope this helps

Answer 2

class MyException(Exception):

    def __str__(self):
        return repr(self.args[0])

e = MyException('asdf')
print e

This is your class in Python2.6 style. The new exception takes an arbitrary number of arguments.

Answer 3

It is unpythonic and useless to create properties that do nothing except getting and setting the value, unchecked and unchanged. The whole point of properties is to allow one to use public attributes freely, until such time as a getter or a setter is actually needed. Then you turn the public attribute into a property, without breaking any client code.

Answer 4

As far as I can tell, simply using a different name for the message attribute avoids the conflict with the base class, and thus stops the deprecation warning:

class MyException(Exception):

def __init__(self, message):
    self.msg = message

def __str__(self):
    return repr(self.msg)

Seems like a hack to me.

Maybe someone can explain why the warning is issued even when the subclass defines a message attribute explicitly. If the base class no longer has this attribute, there shouldn't be a problem.