On 7-12-2009 10:12, Peter Otten wrote:
So there are 2 problems: the pickle protocol isn't used when exception
objects (or instances of classes derived from Exception) are pickled, and
during unpickling, it then
crashes because it calls __init__ with the wrong amount of parameters.
(why is it bothering with __init__ anyway? Aren't exceptions new style
classes?)
The __reduce__() method is called when you pickle an object. It returns an
argument tuple and a factory. For exceptions that factory is the class which
is why __init__() is called when the object is unpickled.
I didn't realize exceptions are treated as "objects pickle know nothing
about" (or 'extension types'). They weren't in Python 2.4 at least :)
So I was expecting them to follow the pickle protocol for normal Python
types, and didn't look past __getnewargs__ and __getinitargs__...
This started happening in Python 2.5, Python 2.4 works without error.
What is causing this?
I think Exceptions need special treatment because they have state that is
not stored in the instance __dict__.
How can I best solve this error?
You could override __reduce__() to call __getstate__(). I don't see the need
for __getnewargs__() because exceptions aren't immutable.
Peter
Thanks, that was enlightening.
I never had to deal with __reduce__ before :)
--irmen
--
http://mail.python.org/mailman/listinfo/python-list
