Dictionaries

Welcome to the Data Structures lesson! Today, we'll learn about dictionaries in Python, which allow you to store data in key-value pairs.

What are Dictionaries?

Dictionaries are collections of items where each item is stored as a pair of a key and a value. They are useful for organizing data in a way that makes it easy to retrieve information based on a unique key.

• Key: A unique identifier for each item.
• Value: The data associated with a key.

Creating a Dictionary

You can create a dictionary by placing items inside curly braces ({}), separated by commas. Each key is separated from its value by a colon (:).

Example:

# Creates a dictionary of student grades
grades = {
    "Alice": 85,
    "Bob": 92,
    "Charlie": 78
}

Accessing Dictionary Values

You can access the value associated with a specific key by using the key inside square brackets ([]) or the get() method.

Example:

# Accesses the grade of Alice using square brackets
print(grades["Alice"])  # Output: 85

# Accesses the grade of Bob using the get() method
print(grades.get("Bob"))  # Output: 92

Adding Items to a Dictionary

You can add new key-value pairs to a dictionary by assigning a value to a new key.

Example:

# Adds a new student to the grades dictionary
grades["Diana"] = 88

# Prints the updated dictionary
print(grades)  # Output: {'Alice': 85, 'Bob': 92, 'Charlie': 78, 'Diana': 88}

Modifying Dictionary Values

Since dictionaries are mutable, you can change the value associated with an existing key.

Example:

# Updates Charlie's grade
grades["Charlie"] = 82

# Prints the updated grade for Charlie
print(grades["Charlie"])  # Output: 82

Removing Items from a Dictionary

You can remove items from a dictionary using the del statement or the pop() method.

Example:

# Removes Bob from the grades dictionary using del
del grades["Bob"]

# Removes Diana from the grades dictionary using pop()
grades.pop("Diana")

# Prints the updated dictionary
print(grades)  # Output: {'Alice': 85, 'Charlie': 82}

Iterating Through a Dictionary

You can loop through a dictionary to access its keys and values using a for loop.

Example:

# Iterates through the dictionary and prints keys and values
for student, grade in grades.items():
    print(student + " scored " + str(grade))
    
# Output:
# Alice scored 85
# Charlie scored 82

Great Job!

You've learned how to use dictionaries to store and manage data in key-value pairs. Dictionaries are powerful tools for organizing information in your Python programs. Keep practicing by creating your own dictionaries and experimenting with their features!