Dictionaries

Dictionaries store data as key/value pairs.

Syntaxperson = {'name': 'Ada', 'age': 36}

A dictionary stores data as key/value pairs. Write it with curly braces and colons. Look up a value by its key.

Working with dictionaries

  • Add or change with d[key] = value.
  • Read safely with d.get(key), which returns None if the key is missing.
  • Loop with d.items(), d.keys(), and d.values().

Example

Example · python
person = {'name': 'Ada', 'age': 36}
print(person['name'])
print(person.get('city'))
person['city'] = 'London'

for key, value in person.items():
    print(key, '=', value)

# Output:
# Ada
# None
# name = Ada
# age = 36
# city = London

When to use it

  • A user profile stores keys like 'name', 'email', and 'age' mapped to their respective values.
  • A word-frequency counter updates a dictionary key's count each time a word is encountered.
  • A cache stores API responses keyed by request URL to avoid redundant network calls.

More examples

Create and access a dictionary

Creates a dict and uses bracket access for known keys and .get() with a default for optional ones.

Example · python
user = {'name': 'Alice', 'age': 30, 'city': 'Oslo'}
print(user['name'])       # Alice
print(user.get('email', 'N/A'))  # N/A (key missing)

Add, update, and delete keys

Shows how to add a new key, update an existing one, and remove a key with del.

Example · python
config = {'debug': False, 'port': 8080}
config['host'] = 'localhost'   # add
config['port'] = 3000          # update
del config['debug']            # delete
print(config)
# {'port': 3000, 'host': 'localhost'}

Iterate over a dictionary

Iterates over key-value pairs using .items() and prints each with an f-string.

Example · python
scores = {'Alice': 92, 'Bob': 85, 'Carol': 98}
for name, score in scores.items():
    print(f'{name}: {score}')

# Output:
# Alice: 92
# Bob: 85
# Carol: 98

Related

py setspy for

Discussion

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