Explain the concept of an iterator and how it is used when traversing data collections.

An iterator is an object that allows sequential traversal of the elements of a collection without exposing its internal structure.

In Python, iterators implement the __iter__() and __next__() methods. When we use a for loop, Python automatically calls these methods to get the next element.

Example of using an iterator:

my_list = [1, 2, 3]
iterator = iter(my_list)  # Get an iterator

print(next(iterator))  # 1
print(next(iterator))  # 2
print(next(iterator))  # 3
# The next call to next(iterator) will raise a StopIteration exception

Iterators are useful because they allow working with large or even infinite sequences, loading elements one by one, saving memory, and simplifying collection traversal code.