An iterable is an object capable of returning its members one at a time. Examples of iterables include all sequence types (list, str, and tuple) and some non-sequence types (dict and file objects), and objects of any classes you define with an __iter__() method or with a __getitem__() method that implements Sequence semantics.
A sequence is an iterable which supports efficient element access using integer indices via the __getitem__() special method and defines a __len__() method that returns the length of the sequence.
An iterator is an object representing a stream of data. Repeated calls to the iterator’s __next__() method [next() method in Python 2] (or passing it to the built-in function next()) return successive items in the stream. When no more data are available a StopIteration exception is raised instead. At this point, the iterator object is exhausted and any further calls to the next() function just raise StopIteration again.
Iterators are required to have an __iter__() method that returns the iterator object itself so every iterator is also iterable and may be used in most places where other iterables are accepted.
A generator is a function which returns a generator iterator. It looks like a normal function except that it contains yield expressions for producing a series of values. Each yield temporarily suspends processing, remembering the location execution state (including local variables and pending try-statements). When the generator iterator resumes, it picks up where it left off (in contrast to functions which start fresh on every invocation).