In the documentation for Py_NewInterpreter(): It is said that :

The return value points to the first thread state created in the new sub-interpreter.  This thread state is made in the current thread state.

I think changing :

This thread state is made in the current thread state.

To:

This thread state is made the current thread state.

Sounds good. Since a call such as:

substate = Py_NewInterpreter()

makes *substate* the current state. no?

The *in* takes me in a different direction of thought.