>_
CodeXPal
šŸ

Dictionaries: Key-Value Pairs

Beginner
90 XP
40 min
Lesson Content

Dictionaries: Storing Key-Value Pairs

Dictionaries are collections of key-value pairs. They're perfect for storing related data where each item has a unique identifier (key).

Creating Dictionaries

Dictionaries use curly braces with key:value pairs:

# Empty dictionary
my_dict = {}

# Dictionary with data
student = {
    "name": "Alice",
    "age": 20,
    "grade": "A"
}

# Using dict() constructor
student = dict(name="Alice", age=20, grade="A")

Accessing Values

Access values using keys:

student = {"name": "Alice", "age": 20}

# Access by key
print(student["name"])  # Alice
print(student["age"])   # 20

# Using get() (safer, returns None if key doesn't exist)
print(student.get("name"))      # Alice
print(student.get("grade"))     # None (key doesn't exist)
print(student.get("grade", "N/A"))  # N/A (default value)

Modifying Dictionaries

Add, update, or remove items:

student = {"name": "Alice", "age": 20}

# Add new key-value pair
student["grade"] = "A"

# Update existing value
student["age"] = 21

# Remove item
student.pop("grade")  # Remove and return value
del student["age"]     # Remove item

Dictionary Methods

student = {"name": "Alice", "age": 20, "grade": "A"}

# Get all keys
print(student.keys())    # dict_keys(['name', 'age', 'grade'])

# Get all values
print(student.values())  # dict_values(['Alice', 20, 'A'])

# Get all items (key-value pairs)
print(student.items())   # dict_items([('name', 'Alice'), ...])

# Check if key exists
print("name" in student)  # True

# Get length
print(len(student))      # 3

Looping Through Dictionaries

student = {"name": "Alice", "age": 20, "grade": "A"}

# Loop through keys
for key in student:
    print(key)

# Loop through keys and values
for key, value in student.items():
    print(f"{key}: {value}")

# Loop through values only
for value in student.values():
    print(value)

Nested Dictionaries

Dictionaries can contain other dictionaries:

students = {
    "alice": {"age": 20, "grade": "A"},
    "bob": {"age": 21, "grade": "B"}
}

print(students["alice"]["grade"])  # A

Common Use Cases

  • šŸ“‹ Storing configuration settings
  • šŸ‘¤ Representing objects/entities (like a user profile)
  • šŸ“Š Counting occurrences (frequency counter)
  • šŸ” Fast lookups by key
Example Code

Create and manipulate a dictionary representing a student.

# Create a student dictionary
student = {
    "name": "Alice",
    "age": 20,
    "major": "Computer Science"
}

# Add a new key 'gpa' with value 3.8
student["gpa"] = 3.8

# Print all information
for key, value in student.items():
    print(f"{key}: {value}")

Expected Output:

name: Alice
age: 20
major: Computer Science
gpa: 3.8
Study Tips
  • ā€¢Read the theory content thoroughly before practicing
  • ā€¢Review the example code to understand key concepts
  • ā€¢Proceed to the Practice tab when you're ready to code