> I'm a bit surprised by the adopted approach. 
> It seems you are merely translating the Python code into C. 
> I think the proper approach for the buffered IO classes would be 
> to use a fixed-size buffer which never gets reallocated.

You are certainly right, but the code io.py is already difficult to understand and 
maintain; the corresponding C code adds one level of complexity;
had I changed the buffering strategy at the same time, it would have been impossible 
to ensure a correct implementation.
Now that my C implementation of the Buffered classes seems correct (all tests pass, 
except a few about destructors) we could try alternative approaches.