We came across this curious phenomenon, when our progam was leaking dynamically created classes.  It started spending CPU, to be fixed when gc  was increased.  The attached .py file demonstrates the problem.

The problem is due to how child classes are added to the parent class, in this case, "object".  Obsolete code tries to look for a NULL pointer in the entire list of children.

In addition, removing child classes is unnecessarily slow.

the attached patch fixes these performance issues.