Python / Dictionaries

PYTHON PROGRAMMING · 14 MIN READ

Dictionaries and key-value lookup

A dictionary maps each unique key to an associated value, making lookup by a meaningful label direct.

Learning objectives

  • Create a dictionary and retrieve a value by key.
  • Handle a missing key intentionally.

Mapping a label to data

PYTHON
student = {"name": "Asha", "score": 86}
print(student["name"])
score = student.get("score", 0)

Here "name" and "score" are keys. Bracket lookup raises KeyError if the key is absent. get instead returns a supplied default—in this example, 0—when the key is missing.

Common mistakes

  • Keys must be hashable; mutable lists cannot be dictionary keys.
  • Do not rely on a key appearing when data comes from an incomplete external source—choose a default or validate it.

Applications and references

Dictionaries model JSON-like records, configuration, lookup tables, and counts.