Assigning to self.__class__

[Paul McGuire]

I have some places in pyparsing where I've found that the most
straightforward way to adjust an instance's behavior is to change its class.
I do this by assigning to self.__class__, and things all work fine.

(Converting to use of __new__ is not an option - in one case, the change is
temporary, and before the end of the function, I change it back again.)

Any comments on this practice?  Is this intended capability for Python
objects, or am I taking advantage of a fortuitous accident, which may get
undone at a future time?

-- Paul