Python Dictionaries Examples

Short, runnable programs that show python dictionaries in action. Read the explanation, press Run, then change the code and try your own ideas. New to the topic? Start with the Python Dictionaries lesson.

1Nested dictionaries

Each user is a dictionary inside the outer dictionary, the same shape as JSON data from an API. Chain keys (and list indexes) to reach the value you need.

Nested dictionaries

users = {
    "u1": {"name": "Asha", "langs": ["Python", "SQL"]},
    "u2": {"name": "Ben", "langs": ["JavaScript"]},
}
print(users["u1"]["name"])
print(users["u2"]["langs"][0])
users["u2"]["langs"].append("Python")
for user_id, info in users.items():
    print(user_id, info["name"], len(info["langs"]))

Expected outputAsha
JavaScript
u1 Asha 2
u2 Ben 2

2Building a dictionary from two lists

zip() pairs items up by position and dict() turns those pairs into keys and values.

Building a dictionary from two lists

countries = ["India", "Japan", "Kenya"]
capitals = ["New Delhi", "Tokyo", "Nairobi"]
capital_of = dict(zip(countries, capitals))
print(capital_of)
print(capital_of["Kenya"])

Expected output{'India': 'New Delhi', 'Japan': 'Tokyo', 'Kenya': 'Nairobi'}
Nairobi

3Grouping words by their first letter

When the values are lists, create an empty list the first time you see a key, then append to it.

Grouping words by their first letter

words = ["apple", "avocado", "banana", "blueberry", "cherry"]
by_letter = {}
for word in words:
    first = word[0]
    if first not in by_letter:
        by_letter[first] = []
    by_letter[first].append(word)
print(by_letter)

Expected output{'a': ['apple', 'avocado'], 'b': ['banana', 'blueberry'], 'c': ['cherry']}

4Merging user settings over defaults

Copy the defaults, then update() with the user's choices: matching keys are overwritten, everything else is kept. The original defaults stay untouched.

Merging user settings over defaults

defaults = {"theme": "light", "font_size": 14, "autosave": True}
user_prefs = {"theme": "dark"}
settings = defaults.copy()
settings.update(user_prefs)
print(settings)
print("Default theme is still", defaults["theme"])

Expected output{'theme': 'dark', 'font_size': 14, 'autosave': True}
Default theme is still light

Practise next

Python Dictionaries exercises → Back to the lesson

Python Dictionary Methods examples Python Nested Data Structures examples Python KeyError: What It Means and How to Fix It examples Working with JSON in Python examples