🐍intermediate

Python Dictionaries — Key-Value Data

Learn to use Python dictionaries to store and retrieve data using keys — like a real-world dictionary but for code.

What is a Dictionary?

A dictionary stores data as key-value pairs. Think of it like a real dictionary: you look up a word (key) and get its definition (value). In code, you might look up a username and get their profile, or look up a product ID and get its price. Dictionaries are one of the most used data structures in Python.

Creating & Using Dictionaries

python

# Create a dictionary
student = {
    "name": "Ishaan",
    "age": 14,
    "grade": "9th",
    "hobbies": ["coding", "chess"]
}

# Access values
print(student["name"])       # "Ishaan"
print(student.get("age"))    # 14
print(student.get("email", "not set"))  # "not set" (default)

# Add/update
student["email"] = "ishaan@example.com"
student["age"] = 15

# Delete
del student["grade"]

# Check if key exists
if "name" in student:
    print("Name found!")

Looping Through Dictionaries

python

scores = {"math": 92, "science": 88, "english": 95}

# Loop through keys
for subject in scores:
    print(subject)

# Loop through values
for score in scores.values():
    print(score)

# Loop through both
for subject, score in scores.items():
    print(f"{subject}: {score}")

# Dictionary comprehension
doubled = {k: v * 2 for k, v in scores.items()}
print(doubled)  # {'math': 184, 'science': 176, 'english': 190}

Pro Tip

Use .get(key, default) instead of dict[key] when you're not sure if the key exists. dict[key] crashes if the key is missing, but .get() returns a default value instead.

Try It Yourself

Create a dictionary that stores 5 countries and their capitals. Write a function that takes a country name and returns its capital. If the country isn't in the dictionary, return 'Country not found'.

Python Basics — Your First Script

Python Variables & Data Types — Storing Information

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