Dictionaries and Sets

Dictionaries

Creating Dictionaries

# Empty dictionary
person = {}
With values
person = {
    "name": "John",
    "age": 30,
    "city": "London"
}

Accessing Values

person = {"name": "John", "age": 30}
print(person["name"])     # John
print(person.get("city")) # London
Default value if key not found
print(person.get("country", "UK"))  # UK

Modifying Dictionaries

person = {"name": "John"}
person["age"] = 31           # Add/update
person["country"] = "UK"     # Add new
del person["age"]            # Delete

Dictionary Methods

person = {"name": "John", "age": 30}
print(person.keys())    # dict_keys(['name', 'age'])
print(person.values()) # dict_values(['John', 30])
print(person.items())  # dict_items([('name', 'John'), ('age', 30)])
Update
person.update({"age": 31, "city": "London"})

Iterating

person = {"name": "John", "age": 30}
for key in person:
    print(f"{key}: {person[key]}")
for key, value in person.items():
    print(f"{key}: {value}")

Sets

Creating Sets

# Empty set
numbers = set()
With values
fruits = {"apple", "banana", "cherry"}

Set Operations

set1 = {1, 2, 3, 4}
set2 = {3, 4, 5, 6}
print(set1.union(set2))        # {1, 2, 3, 4, 5, 6}
print(set1.intersection(set2))  # {3, 4}
print(set1.difference(set2))    # {1, 2}
print(set1.symmetric_difference(set2))  # {1, 2, 5, 6}

Set Methods

fruits = {"apple", "banana"}
fruits.add("cherry")     # Add element
fruits.remove("apple")   # Remove (raises error if not found)
fruits.discard("grape")  # Remove (silent if not found)
fruits.clear()           # Clear all

Summary

• Dictionaries: key-value pairs, fast lookup
• Sets: unique unordered elements, great for membership tests

Next Lesson

In the next lesson, you'll learn about functions.