Dictionaries and Key-Value Access in Python

In Python, a dictionary is a powerful built-in data structure that allows you to store data as key-value pairs. It’s ideal for representing structured information like user profiles, configuration settings, or any data that maps one item to another.

Let’s dive into how dictionaries work and how you can use them effectively in your Python programs.

What is a Dictionary?

A dictionary is defined using curly braces {} with keys and values separated by colons :.

person = {

    "name": "Ali",

    "age": 30,

    "city": "Lahore"

}

Each key must be unique and immutable (like strings, numbers, or tuples). Values can be of any data type.

Accessing Values

You can access a value by referencing its key:

print(person["name"])  # Output: Ali

⚠️ If the key doesn’t exist, Python raises a KeyError.

To avoid errors, use .get():

print(person.get("email"))  # Output: None

You can also provide a default value:

print(person.get("email", "Not Provided"))  # Output: Not Provided

Common Dictionary Methods

• keys() - Returns all keys

• values() - Returns all values

• items() - Returns key-value pairs as tuples

• update() - Adds or updates key-value pairs

• pop(key) - Removes a key and returns its value

• clear() - Removes all items

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

print(person.items())   # dict_items([('name', 'Ali'), ('age', 30), ('city', 'Lahore')])

Looping Through a Dictionary

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}")

Use Cases for Dictionaries

• Storing user data

• Mapping IDs to names

• Counting occurrences

• Representing JSON-like structures

inventory = {

    "apple": 10,

    "banana": 5,

    "orange": 8

}

Practice Challenge

Try this:

student = {

    "name": "Zara",

    "grades": [85, 90, 78]

}

# Access the second grade

print(student["grades"][1])

Summary

Dictionaries are one of the most versatile and efficient data structures in Python. They allow you to organize and retrieve data quickly using meaningful keys.

Next Up: Defining functions with def