# How to Think Like a Computer Scientist: The PreTeXt Interactive Edition

## Section10.24Nested Lists

A nested list is a list that appears as an element in another list. In this list, the element with index 3 is a nested list. If we print(nested[3]), we get [10, 20]. To extract an element from the nested list, we can proceed in two steps. First, extract the nested list, then extract the item of interest. It is also possible to combine those steps using bracket operators that evaluate from left to right.

### Checkpoint10.24.1.

What is printed by the following statements?
alist = [ [4, [True, False], 6, 8], [888, 999] ]
if alist[0][1][0]:
print(alist[1][0])
else:
print(alist[1][1])

• 6
• 6 is in the wrong list. alist[1] refers to the second item in alist, namely [888,999].
• 8
• 8 is in the wrong list. alist[1] refers to the second item in alist, namely [888,999].
• 888
• Yes, alist[0][1][0] is True and alist[1] is the second list, the first item is 888.
• 999
• alist[0][1][0] is True. Take another look at the if statement.