📦 Introduction

Collections: Don't Lose Your Data

So far, we've used variables to store one thing at a time. One name, one number, one boolean. But what if you need to store 100 names? Creating name1, name2, name3... is a terrible idea. Instead, we group them together into a Collection.

A single variable is like carrying one potato. A Collection is like bringing a shopping bag. You can put as many potatoes in the bag as you want! 🥔🛍️

📋 Lists

The humble List

A ListAn ordered collection of items. You create them using square brackets [ ]. is simply an ordered sequence of items. It uses square brackets [].

friends = ["Rahul", "Priya", "Amit"]

To get an item out of the list, you ask for its position (called an index). But beware: Python starts counting at 0, not 1!

lists.py
fruits = ["Apple", "Banana", "Mango"]

print(fruits[0])  # Prints Apple
print(fruits[1])  # Prints Banana

fruits.append("Orange")
print(fruits)print(fruits[0])Index 0 is the FIRST item. Index 1 is the SECOND.
fruits.append(...).append() adds a new item to the very end of the list.

📖 Dictionaries

Storing Key-Value Pairs

Lists are great, but sometimes numbers aren't the best way to look things up. A DictionaryA collection of key-value pairs. You look up the 'key' to find its 'value'. Uses curly braces { }. lets you use a name (a "key") to look up data (a "value"). It uses curly braces {}.

dictionary.py
student = {
    "name": "Sarpanch",
    "age": 5,
    "is_snake": True
}

print(student["name"])  # Prints Sarpanch
student["age"] = 6      # Happy birthday!student = { ... }Dictionaries use curly braces. Inside, it's always key: value.
print(student["name"])Instead of asking for index [0], you ask for the key ["name"].

💡 Real-Life Analogy

A List is like a shelf of numbered jars. You say "Give me jar number 0" or "Put this in the next available space at the end."

A Dictionary is like an actual contact book in your phone. You don't say "Call contact number 42." You say "Call 'Mom'." The Key is the name, the Value is the phone number.

🖼️ Diagram

Lists vs Dictionaries

Lists use numeric indexes (starting at 0). Dictionaries use custom string keys.

😂 Sarpanch's Corner

The Address Book

Panel 1

"I made an address book dictionary!"

book = {"Rahul": "123 Main St"}

Panel 2

"Now to find who lives at 123 Main St..."

print(book["123 Main St"])

Panel 3

"KeyError: '123 Main St'"

You can look up the value using the key, but you can't look up the key using the value!

🚀 Try It Yourself

Collections in Action

Try adding and changing elements in the List and Dictionary.

💡 Challenges:

Use .append() to add your own name to the end of the users list.
Print the 2nd user in the list (Careful! What index is the 2nd user?).
Add a new key to the profile dictionary for "hobby" and print the whole dictionary.

✅ Summary

Grouping Stuff — Done! 📦

Lists use [] and store items in an ordered sequence.
Lists start counting at index 0. The first item is my_list[0].
You can add items to the end of a list using .append("item").
Dictionaries use {} and store data in "key": "value" pairs.
You look up data in a dictionary using its key, like my_dict["name"].

Now you can store massive amounts of data without losing your mind! You're officially a data wrangler. Next, we'll learn how to write our own custom Python functions! 🛠️