[Python-Dev] Is explicit registration of Iterators needed?

[Serhiy Storchaka]

A number of builtin iterator classes (but not all builtin iterator 
classes) are registered with the Iterator ABC in 
Lib/_collections_abc.py.  But isinstance(it, Iterable) check works 
without explicit registration, because Iterable has __subclasshook__ 
that checks iterator methods.  Is there a need in explicit 
registrations?  Or their can be safely removed?