most common usefor number in range( )inefficient to make huge list just for this "iteratoranything that can be treated like list list(iteratorexplicit list so why does the range(function not just produce listwellits most common use is in for loop only one value is required at time if the list was explicitly created would waste computer memory for all the items not in use at the time and computer time for creating them all at once (truth be toldfor the purposes of this course you wouldn' notice