Python Dictionaries

Creating a dictionary

Dictionaries store data as key:value pairs. Keys must be unique and immutable.

person = {
    "name": "Alice",
    "age": 30,
    "city": "NYC"
}
print(person["name"])

Modifying and iterating

Add, update, or delete entries. Loop through keys, values, or items.

d = {"a": 1, "b": 2}
d["c"] = 3
for k, v in d.items():
    print(k, v)

Try it yourself

Run the example below. Edit it and see what changes.

ages = {"Alice": 25, "Bob": 30}
print(ages["Alice"])
ages["Charlie"] = 35
print(ages)
 

Common mistakes

• ⚠Using a non-existent key without .get() raises KeyError.
• ⚠Keys must be immutable (strings, numbers, tuples) — not lists.