16.1. Introduction: Sorting with Sort and Sorted

When we first introduced lists, we noted the existence of a method sort. When invoked on a list, the order of items in the list is changed. If no optional parameters are specified, the items are arranged in whatever the natural ordering is for the item type. For example, if the items are all integers, then smaller numbers go earlier in the list. If the items are all strings, they are arranged in alphabetic order.

L1 = [1, 7, 4, -2, 3] L2 = ["Cherry", "Apple", "Blueberry"] L1.sort() print(L1) L2.sort() print(L2)

Note that the sort method does not return a sorted version of the list. In fact, it returns the value None. But the list itself has been modified. This kind of operation that works by having a side effect on the list can be quite confusing.

In this course, we will generally use an alternative way of sorting, the function sorted rather than the method sort. Because it is a function rather than a method, it is invoked on a list by passing the list as a parameter inside the parentheses, rather than putting the list before the period. More importantly, sorted does not change the original list. Instead, it returns a new list.

L2 = ["Cherry", "Apple", "Blueberry"] L3 = sorted(L2) print(L3) print(sorted(L2)) print(L2) # unchanged print("----") L2.sort() print(L2) print(L2.sort()) #return value is None

You have attempted of activities on this page