Lists: Your First Collection

Lists are compound data types used to group together other values.

fruits = ['apple', 'banana', 'cherry']
print(fruits)

['apple', 'banana', 'cherry']

Mixing Data Types

A powerful feature of Python is that lists might contain items of different types.

mixed_list = [1, 'apple', 3.14, True]
print(mixed_list)

[1, 'apple', 3.14, True]

Changing List Contents

Unlike strings, lists are mutable. This means it is possible to change their content:

scores = [90, 85, 88]
scores[1] = 95
print(scores)

[90, 95, 88]

Appending Items

You can add new items at the end of the list by using the append() method.

colors = ['red', 'green']
colors.append('blue')
print(colors)

['red', 'green', 'blue']

Finding the Length

Just like with strings, the built-in len() function also applies to lists:

names = ['Alice', 'Bob', 'Charlie']
print(len(names))

3

Iterating Over Lists

You can use a for loop to easily go through every item in a list:

items = ['a', 'b', 'c']
for item in items:
    print(item)

a
b
c

Common Misconceptions

List indices start at 1. Python lists are zero-indexed, meaning the first element is at index 0.

You cannot change a list once it is created. Lists are mutable. You can change their elements, add new ones, or remove them.

append() can add multiple items at once. append() takes exactly one argument and adds it as a single element to the end. To add multiple elements from an iterable, use extend().

Edge Cases

• Empty lists [] are completely valid and have a length of 0.
• Appending a list to a list (e.g., a.append([1, 2])) adds the list as a single nested element, rather than flattening it.

Under the Hood

Watch how list modification and appending works in memory step-by-step:

my_list = [10, 20]
my_list[0] = 15
my_list.append(30)