Interpreter & Thread state & Frame structures.

[alessiogiovanni.baroni at gmail.com]

Hi to all,
there are some fields in the PyInterpreterState and PyThreadState
obscures.
PyInterpreterState:
  1) Why there are the fields *next and *tstate_head?

PyThreadState:
  1) Why there is the field *next?

An object PyFrameObject is a portion of code, with a state. But
exactly? Contents of a method/function, or more simply any block
indented of code? For example, this code:
    def foo(s):
        if s > 0:
            return True
        else:
            return False

how much frames are?

Thank you!