Python Lesson 8: Dictionaries

PYTHON

AllComputerss

4/18/20261 min read

Dictionaries are one of Python’s most powerful and flexible data structures. They allow you to store data in key-value pairs, making it easy to organize and retrieve information efficiently.

What Are Dictionaries?

A dictionary is an unordered collection where each item consists of a key and a value. Keys must be unique and immutable (like strings or numbers), while values can be of any data type.

Creating Dictionaries

# Example of a dictionary

person = { "name": "Alice", "age": 25, "city": "Paris" }

print(person)

Accessing Values

You can access values by referencing their keys:

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

print(person["age"]) # Output: 25

Adding and Updating Items

Dictionaries are mutable, so you can add new key-value pairs or update existing ones:

person["email"] = "alice@example.com" # Add new key-value pair

person["age"] = 26 # Update existing value print(person)

Removing Items

You can remove items using del or the pop() method:

del person["city"]

print(person)

person.pop("email")

print(person)

Iterating Through Dictionaries

You can loop through keys, values, or both:

for key in person:

print(key, person[key])

for key, value in person.items():

print(f"{key}: {value}")

Useful Dictionary Methods

keys() → Returns all keys
values() → Returns all values
items() → Returns key-value pairs
get(key) → Safely retrieves a value without error if the key doesn’t exist

print(person.get("name")) # Output: Alice

print(person.keys()) # Output: dict_keys(['name', 'age'])

Why Use Dictionaries?

Fast lookups: Accessing values by keys is efficient.
Flexible storage: Values can be any type, including lists or other dictionaries.
Real-world use cases: Perfect for representing structured data like user profiles, configuration settings, or JSON objects.

Conclusion

Dictionaries are essential for organizing and managing data in Python. Their key-value structure makes them ideal for scenarios where quick lookups and structured information are needed. Mastering dictionaries will prepare you for working with more complex data formats and APIs.