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

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.

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

The advice to use str(myexception) leads to unicode problems in python 2.7, e.g.:

str(Exception(u'δσφφδσ'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-5: ordinal not in range(128)

:(

unicode(Exception(u'δσφφδσ')) 

works as expected, and is preferred in cases where some of the content of the error string includes user input

Answer 4

Continuing on from geekQ's answer, the preferred code replacement depends on what you need to do:

### Problem
class MyException(Exception):
    """My documentation"""

try:
    raise MyException('my detailed description')
except MyException as my:
    ### Solution 1, fails in Python 2.x if MyException contains                                                                     

                                                        
            

查看更多

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Answer 5

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 6

Solution - almost no coding needed

Just inherit your exception class from Exception and pass the message as the first parameter to the constructor

Example:

class MyException(Exception):
    """My documentation"""

try:
    raise MyException('my detailed description')
except MyException as my:
    print my # outputs 'my detailed description'

You can use str(my) or (less elegant) my.args[0] to access the custom message.

Background

In the newer versions of Python (from 2.6) we are supposed to inherit our custom exception classes from Exception which (starting from Python 2.5) inherits from BaseException. The background is described in detail in PEP 352.

class BaseException(object):

    """Superclass representing the base of the exception hierarchy.
    Provides an 'args' attribute that contains all arguments passed
    to the constructor.  Suggested practice, though, is that only a
    single string argument be passed to the constructor."""

__str__ and __repr__ are already implemented in a meaningful way, especially for the case of only one arg (that can be used as message).

You do not need to repeat __str__ or __init__ implementation or create _get_message as suggested by others.