Dictionaries

:dart: Learning Objectives

By the end of this lesson, you'll be able to:

• Understand what dictionaries are and why we use them
• Create dictionaries with key-value pairs
• Access, change, add, and remove items in dictionaries
• Work with nested dictionaries for complex data

:information_source: What is a Dictionary? A dictionary is a data structure that stores information using key-value pairs. Think of it like a real dictionary where you look up a word (key) to find its meaning (value)!

:books: Why Use Dictionaries?

Dictionaries help us store data in a meaningful way. Let's see why they're better than lists for certain tasks.

The Problem with Lists

Imagine you want to store information about a student. Using a list might look like this:

student = ["Sharvin", "M", 20]

What does each value mean? It's not clear! :emoji:

The Dictionary Solution

Python solves this problem with dictionaries:

student = {"name":"Sharvin", "gender":"M", "age":20}

Now we can see exactly what each piece of information means! :tada:

:emoji:️ Dictionary Structure

A dictionary has a simple structure:

• Dictionary name: The variable that stores your dictionary
• Curly brackets { }: Contains all the key-value pairs
• Commas ,: Separate each key-value pair
• Colons :: Connect each key to its value

Example: Number Names Dictionary

:memo: Important! Dictionaries don't keep items in order like lists do. Each item is found by its key, not by its position.

:hammer_and_wrench: Working with Dictionaries

Let's learn the five main operations you can do with dictionaries:

1. Create - Make a new dictionary
2. Access - Get values from the dictionary
3. Change - Update existing values
4. Add - Put new items in the dictionary
5. Remove - Delete items you don't need

1️⃣ Create Dictionary

Creating a dictionary is easy! Just use curly brackets and add your key-value pairs:

student = {
    "name": "Chong Wei",
    "gender": "M",
    "age": 15
}

:bulb: Pro Tip! Write each key-value pair on a new line to make your dictionary easier to read! This makes it much easier to see what information you're storing.

2️⃣ Access Items in Dictionary

There are several ways to get information from your dictionary. Let's explore each method!

Getting a Single Value

To get a value, use the key inside square brackets []:

student["name"]

student = {
    "name":"Chong Wei",
    "gender":"M",
    "age":15
}
print(student["name"])

Expected output:

Chong Wei

Getting Multiple Items

Python gives us special methods to access different parts of a dictionary:

• .items() - Get all key-value pairs together (perfect for looping!)
• .keys() - Get all the keys only (useful to see what information is stored)
• .values() - Get all the values only (helpful for getting just the data)

student.items()
student.keys()
student.values()

student = {
    "name":"Chong Wei",
    "gender":"M",
    "age":15
}
print(student.items())
print(student.keys())
print(student.values())

Expected output:

dict_items([('name', 'Chong Wei'), ('gender', 'M'), ('age', 15)])
dict_keys(['name', 'gender', 'age'])
dict_values(['Chong Wei', 'M', 15])

Checking if a Key Exists

Before using a key, you can check if it exists:

"gender" in student

student = {
    "name":"Chong Wei",
    "gender":"M",
    "age":15
}
print("gender" in student)

Expected output:

True

:memo: Note This returns True if the key exists, and False if it doesn't!

Looping Through a Dictionary

You can use a for loop to go through all items:

for x in student.items():
    print(x)

student = {
    "name":"Chong Wei",
    "gender":"M",
    "age":15
}
for x in student.items():
    print(x)

Expected output:

('name', 'Chong Wei')
('gender', 'M')
('age', 15)

Each item is printed as a tuple (a pair of values).

3️⃣ Change Item in Dictionary

Changing a value is simple - just assign a new value to an existing key:

student["age"] = 16
print(student)

Expected output:

{'name': 'Chong Wei', 'gender': 'M', 'age': 16}

The age changed from 15 to 16! :emoji:

4️⃣ Add Item in Dictionary

Adding a new item works the same way - just use a new key:

student["Program"] = "F"
print(student)

Expected output:

{'name': 'Chong Wei', 'gender': 'M', 'age': 16, 'program': 'F'}

Now the dictionary has a new key-value pair! :sparkles:

5️⃣ Remove Item in Dictionary

To remove an item, use the del keyword:

del student["gender"]
print(student)

Expected output:

{'name': 'Chong Wei', 'age': 16, 'program': 'F'}

The "gender" key and its value are gone! :emoji:️

:emoji: Nested Data Structures

Sometimes you need to store complex data. You can put dictionaries inside dictionaries, or lists inside dictionaries!

Example: Multiple Students Data

We can store this data in two ways:

Method 1: Dictionaries in Dictionary (Each student is a separate dictionary)

Students = {
    "student1": {
        "name":"Chong Wei",
        "gender": "M",
        "age":15
    },
    "student2": {
        "name":"Sharvin",
        "gender": "M",
        "age":12
    },
    "student3": {
        "name":"Yet Phing",
        "gender": "F",
        "age":13
    }
}

Method 2: Lists in Dictionary (Each attribute contains a list of values)

Students = {
    "name":["Chong Wei","Sharvin","Yet Phing"],
    "gender":["M", "M", "F"],
    "age":[15,12,13]
}

:bulb: Tip Both methods work! Choose Method 1 when you need to access all information about one student. Choose Method 2 when you need to work with one type of information for all students.

:emoji: Learn More: Nested Dictionary Tutorial

:memo: Summary

Dictionaries are powerful tools for organizing data:

• They store information as key-value pairs
• You can create, access, change, add, and remove items easily
• They're perfect for storing related information together
• You can even put dictionaries inside dictionaries for complex data!

:movie_camera: Video Lesson

:emoji: Practice with AI

Code with AI: Try using AI to work with dictionaries.

Prompts to try:

• "Create a Python dictionary to store information about a student (name, age, grades)."
• "How can I access a value in a nested dictionary using Python?"
• "Show me how to loop through a dictionary and print all values."
• "Create a dictionary of your favorite foods with categories as keys."

:dart: Practice Tasks

Try these exercises to master dictionaries:

1. Create Your Profile: Make a dictionary with your name, age, favorite subject, and hobby
2. School Inventory: Create a nested dictionary to store information about different classrooms and their equipment
3. Grade Tracker: Build a dictionary that stores student names as keys and their grades as values
4. Dictionary Explorer: Take any dictionary and practice accessing items using .keys(), .values(), and .items()

:memo: Remember! Dictionaries are like labeled boxes - each label (key) helps you find exactly what you're looking for (value). Practice makes perfect! :star2: