Lists, Ordered Collections

Store and manipulate multiple values in a single variable

A list stores multiple values in order. Think of it as a shopping cart, you can add items, remove items, and look up any item by its position.

Creating and accessing listspython

numbers = [3, 1, 4, 1, 5, 9]
names = ["Alice", "Bob", "Charlie"]

print(numbers[0])    # 3  (first item)
print(numbers[-1])   # 9  (last item)
print(len(numbers))  # 6  (length)
print(numbers[1:4])  # [1, 4, 1]  (slice)

🔍Code TracerStep 1 / 7

trace.py

1nums = [3, 1, 4, 1, 5]←

2nums.append(9)

3nums.sort()

4print(nums)

Variables

No variables yet

Step 1 / 7

Modifying listspython

fruits = ["apple", "banana"]

fruits.append("cherry")     # Add to end
fruits.insert(0, "avocado") # Insert at position
fruits.remove("banana")     # Remove by value
popped = fruits.pop()       # Remove & return last item
fruits.sort()               # Sort in place
print(fruits)

Common list operations:

list.append(x), add to end

list.insert(i, x), insert at index i

list.remove(x), remove first occurrence of x

list.pop(), remove and return last item

list.sort(), sort in place

sorted(list), return new sorted list

🌍In the Real World...

Container logs come as lists of strings. Pod names, node IPs, deployment replicas, security group rules, all stored and manipulated as lists in cloud automation scripts.

Practice Exercises

0/2 solved

Exercise 1 of 2medium

⏱ 00:00

Second Largest

Write a function second_largest(numbers) that returns the second largest unique number in a list.
Example: second_largest([3, 1, 4, 1, 5, 9, 2, 6]) → 6

solution.py

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Exercise 2 of 2medium

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Flatten a List

Write a function flatten(nested) that takes a list of lists and returns a single flat list.
Example: flatten([[1,2], [3,4], [5]]) → [1, 2, 3, 4, 5]

solution.py

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Solve all 2 exercises to unlock completion

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