Advanced Python · Week 2

Dictionaries

Step 1 of 5

Exercise 1: Introduction to Dictionaries

Welcome to Python 2, Lesson 2! Today, we'll learn about dictionaries, a powerful and flexible data structure in Python.

What is a Dictionary?

A dictionary is an unordered collection of key-value pairs. It's also known as an associative array, hash table, or hash map in other programming languages.

Here's how to create a simple dictionary:

# Create a dictionary of fruit colors
fruit_colors = {
    "apple": "red",
    "banana": "yellow",
    "grape": "purple"
}

print(fruit_colors)
            

Now it's your turn! Create a dictionary called student_scores with the following information:

Alice: 85
Bob: 92
Charlie: 78

After creating the dictionary, print it to see the result.

Starter code

# Create the student_scores dictionary here

# Print the dictionary

Write your code here

Exercise 2: Accessing and Modifying Dictionaries

Now that we've created a dictionary, let's learn how to access and modify its contents.

Accessing and Modifying Dictionaries

Access a value: dict_name[key]
Modify a value: dict_name[key] = new_value
Add a new key-value pair: dict_name[new_key] = value

Here's an example:

fruit_colors = {"apple": "red", "banana": "yellow", "grape": "purple"}

# Access a value
print(fruit_colors["banana"])

# Modify a value
fruit_colors["apple"] = "green"

# Add a new key-value pair
fruit_colors["orange"] = "orange"

print(fruit_colors)
            

Your turn! Using the student_scores dictionary from the previous exercise:

Print Charlie's score
Update Bob's score to 95
Add a new student, David, with a score of 88
Print the updated dictionary

Starter code

student_scores = {
    "Alice": 85,
    "Bob": 92,
    "Charlie": 78
}

# Your code here

Write your code here

Exercise 3: Dictionary Methods

Dictionaries come with several useful methods that make working with them easier.

Common Dictionary Methods

dict.keys(): Returns a list of all keys
dict.values(): Returns a list of all values
dict.items(): Returns a list of all key-value pairs as tuples
dict.get(key, default): Returns the value for a key, or a default if the key doesn't exist

Here's an example:

fruit_colors = {"apple": "red", "banana": "yellow", "grape": "purple"}

print("Keys:", fruit_colors.keys())
print("Values:", fruit_colors.values())
print("Items:", fruit_colors.items())
print("Color of cherry:", fruit_colors.get("cherry", "unknown"))
            

Your task:

Print all the student names (keys) in the student_scores dictionary
Print all the scores (values) in the dictionary
Print all the student-score pairs (items)
Try to get the score for a student named "Eve". If Eve doesn't exist, return "Not found" as the default value

Starter code

student_scores = {
    "Alice": 85,
    "Bob": 95,
    "Charlie": 78,
    "David": 88
}

# Your code here

Write your code here

Exercise 4: Looping Through Dictionaries

Often, you'll need to iterate through all the key-value pairs in a dictionary. Python provides several ways to do this.

Looping Through Dictionaries

Loop through keys: for key in dict:
Loop through values: for value in dict.values():
Loop through key-value pairs: for key, value in dict.items():

Here's an example:

fruit_colors = {"apple": "red", "banana": "yellow", "grape": "purple"}

# Loop through keys
for fruit in fruit_colors:
    print(f"Fruit: {fruit}")

# Loop through values
for color in fruit_colors.values():
    print(f"Color: {color}")

# Loop through key-value pairs
for fruit, color in fruit_colors.items():
    print(f"The {fruit} is {color}")
            

Your task:

Loop through the student_scores dictionary and print each student's name
Calculate and print the average score of all students
Find and print the name of the student with the highest score

Starter code

student_scores = {
    "Alice": 85,
    "Bob": 95,
    "Charlie": 78,
    "David": 88
}

# Your code here

Write your code here

Weekly Project: Contact Book

Let's put everything we've learned about dictionaries into practice by creating a simple contact book application.

Your task is to create a program that allows users to:

Add a new contact (name and phone number)
View all contacts
Search for a contact by name
Update a contact's phone number
Delete a contact

Here's a starting template:

def add_contact(contacts, name, phone):
    # Your code here
    pass

def view_contacts(contacts):
    # Your code here
    pass

def search_contact(contacts, name):
    # Your code here
    pass

def update_contact(contacts, name, new_phone):
    # Your code here
    pass

def delete_contact(contacts, name):
    # Your code here
    pass

# Main program
contacts = {}

while True:
    print("\n1. Add contact")
    print("2. View all contacts")
    print("3. Search contact")
    print("4. Update contact")
    print("5. Delete contact")
    print("6. Exit")
    
    choice = input("Enter your choice (1-6): ")
    
    # Implement the menu options here
    
    if choice == '6':
        break

print("Thank you for using the Contact Book!")
            

Implement the functions and the main program loop. Use the dictionary methods and loops we've learned to manage the contacts.

This project will give you hands-on experience with dictionaries and reinforce the concepts we've covered this week. Good luck!

Starter code

# Implement your Contact Book application here

Write your code here

PreviousList Review and Algorithms NextTuples