Some subclasses of Exception are no longer pickleable in Python 2.5. An
example:
class A(Exception):
def __init__(self, foo):
self.foo = foo
The key problem here is if you do not somehow set self.args to the correct
arguments (via Exception.__init__ or setting self.args directly), you will
get a TypeError when you try to unpickle it:
TypeError: __init__() takes exactly 2 arguments (1 given)
I do not think this is unusual. I found a few examples in Python's
standard library that have this problem:
subprocess.CalledProcessError
HTMLParser.HTMLParseError
httplib.UnknownProtocol, httplib.IncompleteRead, httplib.BadStatusLine
optparse.OptParseError
pickle._Stop
and on and on...
Does anyone have any thoughts about this? Is it a bug?
I can imagine one could argue that exceptions should call the base
__init__ method to properly set args, but there are so many exceptions out
there that do not do this that it would be very difficult to track them
all down.
I removed the __reduce__ and __setstate__ methods from BaseException and
everything seems to just work. Pickling/unpickling works for all
protocols whether or not you set self.args. Is this an appropriate
solution? I'm not sure what the motivation for having these methods is.
-Eric
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