Dictionaries

A dictionary is a collection of key-value pairs, where you look a value up by its key instead of by its position.

Last updated: 30 Sep, 2026 · Python 3.14

A ticket is more than its text: it has an id and a customer too. A list would keep them by position; a dictionary gives each one a name.

my_dict = {"Car1": "Audi", "Car2": "BMW", "Car3": "Mercedes Benz"}
print(my_dict["Car1"])

for x in my_dict:
    print(x)
for x in my_dict.values():
    print(x)
for x in my_dict.items():
    print(x)

my_dict["car4"] = "Audi 2.0"
my_dict["Car1"] = "Maruti"
print(my_dict)

Audi
Car1
Car2
Car3
Audi
BMW
Mercedes Benz
('Car1', 'Audi')
('Car2', 'BMW')
('Car3', 'Mercedes Benz')
{'Car1': 'Maruti', 'Car2': 'BMW', 'Car3': 'Mercedes Benz', 'car4': 'Audi 2.0'}

Looping over a dictionary gives its keys; values() gives the values and items() gives both as pairs. A new key, car4, was added at the end, and storing under Car1 again replaced Audi with Maruti. The spelling of the car names is tidied from the notebook. A ticket works the same way, with a key for each field.

Syntax:

record = {"key": value, "other_key": other_value}
record["key"]            # read a value
record["new_key"] = x    # add or replace

Creating a dictionary and reading values

ticket = {"id": 1, "customer": "Asha", "text": "I was charged twice for one order"}
print(ticket["text"])
print(ticket["customer"])

I was charged twice for one order
Asha

Curly brackets make a dictionary. Each entry is a key, a colon, and a value. You read a value by putting its key in square brackets, the way a list takes a position.

Adding and changing values

ticket["category"] = "billing"
ticket["customer"] = "Asha K."
print(ticket)

{'id': 1, 'customer': 'Asha K.', 'text': 'I was charged twice for one order', 'category': 'billing'}

Storing under a key that does not exist adds it. Storing under one that does replaces the value. A key appears only once in a dictionary.

Reading a key that is not there

print(ticket["priority"])

Traceback (most recent call last):
  File "main.py", line 1, in <module>
    print(ticket["priority"])
KeyError: 'priority'

A missing key is a KeyError. When a key may or may not be there, use get, which gives back a value you choose instead of stopping the program. Delete that line before you add the next example: an error stops the file where it happens.

print(ticket.get("priority"))
print(ticket.get("priority", 3))
print(ticket.get("customer", "unknown"))

None
3
Asha K.

None is Python's value for nothing here. get gives it back when you do not name a default.

Looping over keys and values

for key, value in ticket.items():
    print(key, "=", value)

id = 1
customer = Asha K.
text = I was charged twice for one order
category = billing

items gives each key with its value, in the order they were added. keys() gives only the keys and values() only the values.

ticket["key"] vs ticket.get("key")

Where dictionaries show up in AI code

• A single chat message: {"role": "user", "content": "..."}.
• Settings passed to a model call, such as a temperature and a token limit.
• The parsed answer of a model that replied in JSON.

Related

• Previous: for loops
• Next: Lists of dictionaries
• Reference: Dictionaries in the Python tutorial