Nested dictionary in Python

A dictionary value can be another dictionary. This is a nested dictionary, and it is the usual way to store a record that has groups of details, such as an employee and their address.

The program

employee = {
    "name": "Grace",
    "role": "Engineer",
    "address": {"city": "London", "postcode": "EC1A 1BB"},
}

print(employee["name"])
print(employee["address"]["city"])

employee["address"]["city"] = "Manchester"
print(employee["address"])

print(employee.get("salary", "Not set"))
print(employee.get("phone", {}).get("mobile", "No mobile"))

Grace
London
{'city': 'Manchester', 'postcode': 'EC1A 1BB'}
Not set
No mobile

How it works

• employee["address"] gives the inner dictionary. Adding ["city"] after it reads a key from that inner dictionary.
• The same chain on the left of = changes the inner value.
• employee["salary"] would raise a KeyError, because there is no such key. get("salary", "Not set") returns the default instead.
• For a key that may be missing two levels down, get("phone", {}) returns an empty dictionary when phone is missing, so the second .get() still works.

Looping over nested data

team = {
    "Ada": {"age": 36, "city": "London"},
    "Linus": {"age": 28, "city": "Helsinki"},
    "Hedy": {"age": 41, "city": "Vienna"},
}

for name, info in team.items():
    print(f"{name} is {info['age']} and lives in {info['city']}")

Ada is 36 and lives in London
Linus is 28 and lives in Helsinki
Hedy is 41 and lives in Vienna

Inside the f-string, the keys use single quotes because the f-string itself uses double quotes.