Dictionaries: values with names

A ticket is more than its text: it has an id and a customer too. A dictionary keeps several values together and gives each one a name, called a key.

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

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

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

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.

A key that is not there

print(ticket["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.

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

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

Looping over a dictionary

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

items gives each key with its value, in the order they were added.