xSkill: notes, lectures and practice for CBSE and CSE

A list is an ordered collection of values, written in square brackets with commas between items. The order matters because each item has a position. Lists can grow and shrink, so they suit a row of names or a set of scores. A list may hold values of different types, though a list of related values is easier to work with.

python

fruits = ['mango', 'pear', 'guava']
print(fruits[0])
print(fruits[-1])
print(len(fruits))

Output

mango
guava
3

5.1 Indexing and slicing Indexes start at 0, so the first item is items[0] . A slice copies part of the list: items[1:3] contains positions 1 and 2, and stops before 3 . Slicing returns a new list, while indexing returns the item stored at that position. 5.2 Changing the list in place append() adds an item at the end. insert() adds an item at a chosen position. pop() removes an item and returns it.

python

tasks = ['read', 'write']
tasks.append('rest')
tasks[0] = 'review'
print(tasks)

Output

['review', 'write', 'rest']

5.3 Common mistake tasks = tasks.append('rest') looks like it updates the list, but it sets tasks to None . append() adds the item and returns None, so the assignment throws away the list name. Call append() on its own line, then continue using the same list name.

python

scores = [72, 85, 91, 64]
print(scores[1:3])
print(sum(scores))
print(max(scores))

Output

[85, 91]
312
91

5.4 Practice Make a list of four tasks and add a fifth with append() . Replace the second task, then remove the last one with pop() . Print the final list and its length after each change, then try reading index 10 and read the error message.