Jakub,

I have attached a revision to the patch.
You are right, when __iter__ returns self.fp (as in previous patch), the
__next__ is superflous. 
But, I was thinking of __iter__ returning an instance of addbase,
instead of self.fp and in that case __next__ was required. But I see
that i had not changed self.fp to self. 

This is implemented in the similar lines of  IOBase class, io.py
w.r.t to your other comment, why do you think __next__ implementation is
incorrect?

Thanks,
Senthil