In Python 2.x, the built-in range() function returns a list of integers, which can consume a lot of memory for large ranges. This behavior was changed in Python 3.x, where range() returns a "range object" instead of a list. This change was made for efficiency reasons, as generating a list is unnecessary for many use cases and can be wasteful in terms of both memory and computation.

However, it is important to note that a range object is not the same as an iterator. An iterator is an object that can be used to iterate over a sequence of values, but does not necessarily store those values in memory. In contrast, a range object represents a sequence of values that can be accessed in a similar manner to a list, but only generates the values as they are needed.

Despite not being an iterator, range objects are still iterable and can be used in a for loop or with other functions that accept iterable objects, such as sum() or list(). Additionally, to obtain an iterator object from a range object, one can use the built-in iter() function.

Overall, the decision to make range() return a range object rather than a list in Python 3.x was a trade-off between memory efficiency and ease of use, and allows for more flexibility and control when dealing with large ranges.