Python Lesson 11: Lists

A list stores multiple values in a single variable, in order. Lists are the most commonly used data structure in Python.

Creating Lists

fruits = ["apple", "banana", "cherry"]
scores = [95, 87, 92, 78, 100]
empty = []

print(fruits)         # ['apple', 'banana', 'cherry']
print(len(fruits))    # 3 — number of items

Accessing Items (Indexing)

fruits = ["apple", "banana", "cherry", "date"]
#           0         1         2        3

print(fruits[0])    # apple (first item)
print(fruits[1])    # banana
print(fruits[-1])   # date (last item)
print(fruits[-2])   # cherry (second from end)

Slicing

numbers = [10, 20, 30, 40, 50, 60]

print(numbers[1:4])   # [20, 30, 40]
print(numbers[:3])    # [10, 20, 30]
print(numbers[3:])    # [40, 50, 60]
print(numbers[::2])   # [10, 30, 50] — every 2nd item

Modifying Lists

fruits = ["apple", "banana", "cherry"]

fruits.append("date")        # add to end
fruits.insert(1, "avocado")  # insert at index 1
fruits.remove("banana")      # remove by value
popped = fruits.pop()        # remove and return last item
fruits[0] = "mango"          # change existing item

print(fruits)

Useful List Methods

numbers = [3, 1, 4, 1, 5, 9, 2, 6]

numbers.sort()           # sort in place
numbers.reverse()        # reverse in place
print(sum(numbers))      # 31
print(min(numbers))      # 1
print(max(numbers))      # 9
print(numbers.count(1))  # 2 — count occurrences
print(numbers.index(5))  # find index of value

Looping with enumerate()

scores = [85, 92, 78, 95, 88]
for i, score in enumerate(scores):
    print(f"Student {i+1}: {score}")