The purely functional viewpoint is that all of our iterables can be processed with recursive functions, where the state is merely the recursive call stack. Pragmatically, Python iterables will often involve evaluation of other for loops. There are two common situations: collection objects and iterables. When working with a collection object, an iterator object is created by the for statement. When working with a generator function, the generator function is an iterator and maintains its own internal state. Often, these are equivalent, from a Python programming perspective. In rare cases—generally those situations where we have to use an explicit next() function—two won't be precisely equivalent.
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