Adding instance attributes to types

[khughes]

I have written a C module which implements a new Python type, and
implemented data attributes for the type using PyGetSetDef/tp_getset.
However, I want to allow instances of this type to have additional data
attributes which also have get() and set() functions. (This might be
better suited to use inherited classes or types, but the differences
would be very minor). Is this possible?