Lists: The Robot’s Backpack
Learn how to store collections of data in lists using the robot’s backpack analogy. Add, remove, and read items from list slots.
Welcome back, coder! 🎒
So far, our variables have been like single cardboard boxes that can only hold one thing at a time. But what if your game character is going on a big adventure and needs to carry a map, a health potion, and a shield? Creating separate variables like item1, item2, and item3 would be a mess!
Instead, we can give our robot a single Backpack that holds a whole list of items. In Python, this is called a List!
What is a List? (The Labeled Backpack)#
Think of a list as a backpack with numbered compartments (or slots) inside it.
- The first slot is 0 (not 1!). In coding, we almost always start counting from zero.
- The second slot is 1, the third is 2, and so on.
graph LR
subgraph Backpack ["🎒 backpack = ['Map', 'Potion', 'Shield']"]
Slot0["Slot [0]: 🗺️ Map"]
Slot1["Slot [1]: 🧪 Potion"]
Slot2["Slot [2]: 🛡️ Shield"]
end
In Python, we write a list using square brackets [ ] and separate the items with commas:
backpack = ["Map", "Potion", "Shield"]Accessing Items (Looking Inside the Slots)#
To ask the robot to pull an item out of a specific slot, we write the name of the list followed by the slot number in square brackets:
print(backpack[0]) # The robot prints "Map" 🗺️
print(backpack[2]) # The robot prints "Shield" 🛡️If we ask for backpack[3], the robot will get confused and crash because there is no slot 3!
Managing Your Backpack (List Tricks)#
As the adventure goes on, our backpack contents will change. Here are three tricks to manage it:
1. Packing a New Item (append)#
To add a new item to the end of the list, use .append():
backpack.append("Sword")
print(backpack) # Prints: ['Map', 'Potion', 'Shield', 'Sword'] ⚔️2. Unpacking/Removing an Item (remove)#
To throw away an item, use .remove():
backpack.remove("Potion")
print(backpack) # Prints: ['Map', 'Shield', 'Sword'] (The Potion is gone!)3. Counting Your Items (len)#
To see how full your backpack is, ask Python to check its length using len():
print(len(backpack)) # The robot counts the items and prints 3Try It Yourself! 🎮#
Open your Python playground and try this code adventure:
snacks = ["Apple", "Cookie"]
print("Original snacks:", snacks)
# 1. Pack a banana!
snacks.append("Banana")
# 2. Eat the cookie!
snacks.remove("Cookie")
# 3. Print the final list
print("Leftover snacks:", snacks)
print("Number of snacks left:", len(snacks))Run the code to see if the robot correctly tells you what is left in your snack bag!
Next time, we will explore Turtle Graphics, where we will command a virtual turtle to draw colorful shapes on our screen. See you then!