Python Dictionaries

Data Types Focus

Python Dictionaries

Dictionaries map keys to values with O(1) lookups on average. Learn how to create, update, iterate, and merge them responsibly.

Iterate effectivelyMerge cleanly

Creation

user = {"id": "42", "active": True}
config = dict(debug=True, retries=3)

Keys must be hashable. Strings, numbers, and tuples are common choices.

Access

user["id"]
user.get("email", "unknown")

Use get to avoid KeyError when missing keys are acceptable.

Iteration

for key, value in user.items():
    ...

.keys() and .values() provide views that update automatically as the dict changes.

Merging

merged = {**defaults, **overrides}
# Python 3.9+
merged = defaults | overrides

Later keys override earlier ones.

Next up in your learning path

Sets and lists interplay

Use sets/lists alongside dicts for advanced data structures.

Companion

JSON serialization

Write dictionaries to disk via json module.

Practice

Comprehensions

Generate dictionaries from iterables in one expression.

Tip