Dictionaries and Sets - Key-Value and Unique Collections

Dictionaries

Dictionaries store key-value pairs.

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

# Accessing values
print(student["name"])  # John

# Adding/Updating
student["gpa"] = 3.8

# Dictionary methods
student.keys()    # Get all keys
student.values()  # Get all values
student.items()   # Get key-value pairs

# Dictionary comprehension
squares = {x: x**2 for x in range(5)}

Sets

Sets are unordered collections of unique items.

# Creating a set
colors = {"red", "green", "blue"}

# Adding elements
colors.add("yellow")

# Removing elements
colors.remove("red")

# Set operations
set1 = {1, 2, 3}
set2 = {2, 3, 4}

union = set1 | set2          # {1, 2, 3, 4}
intersection = set1 & set2   # {2, 3}
difference = set1 - set2     # {1}

When to Use What

• Lists: Ordered, mutable, allows duplicates
• Tuples: Ordered, immutable, allows duplicates
• Dictionaries: Key-value pairs, fast lookups
• Sets: Unique items, fast membership testing