What is a Dictionary?

# Syntax
my_dict = {
    "key1": "value1",
    "key2": "value2"
}

Example:

student = {
    "name": "Alice",
    "age": 22,
    "course": "Computer Science"
}

Dictionary Basics

1. Accessing Values

print(student["name"])   # Output: Alice

You can also use .get() which avoids an error if the key doesn't exist:

print(student.get("email", "Not Found"))  # Output: Not Found

2. Modifying Values

student["age"] = 23

3. Adding New Key-Value Pair

student["email"] = "alice@example.com"

4. Removing Elements

student.pop("course")  # Removes 'course' key

🔹 Dictionary Methods

Example:

print(student.keys())    # dict_keys(['name', 'age', 'email'])
print(student.values())  # dict_values(['Alice', 23, 'alice@example.com'])
print(student.items())   # dict_items([('name', 'Alice'), ...])

Dictionary Types (Based on Structure)

1. Nested Dictionary

A dictionary inside another dictionary.

students = {
    "101": {"name": "Alice", "age": 22},
    "102": {"name": "Bob", "age": 24}
}

print(students["101"]["name"])  # Output: Alice

2. Empty Dictionary

empty_dict = {}

3. Using dict() Constructor

data = dict(name="John", age=30)
print(data)  # {'name': 'John', 'age': 30}

4. Dictionary with Mixed Data Types

info = {
    "name": "Alice",
    "age": 25,
    "marks": [85, 90, 92],
    "is_graduated": True
}

5. Dictionary with Tuple Keys

Keys must be immutable — so tuples are allowed.

location = {
    (10.4, 20.3): "Point A",
    (11.5, 22.1): "Point B"
}

Looping Through a Dictionary

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

Dictionary Comprehension

squares = {x: x*x for x in range(1, 6)}
print(squares)  # {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Summary Table