sorted and key Functions

Scenario: Incidents must be ordered by severity rather than alphabetically.

New words, in plain English

• key function - a function returning the comparison value for each item
• Stable sort - equal-key items keep their original order
• Callable - anything that can be called with parentheses

sorted returns a new list; .sort() changes a list. Pass key= to explain what matters and reverse=True for descending order.

Analogy: A Python program is like a clear set of instructions for a careful helper: names label things, indentation groups steps, and errors explain where the helper became confused.

A small, real example

events = [{"name": "disk", "severity": 3}, {"name": "cpu", "severity": 1}]
ordered = sorted(events, key=lambda event: event["severity"], reverse=True)

Tip: Use operator.itemgetter or attrgetter when it makes a repeated key clearer.

Goal: Practice this idea in the py-list-comprehension challenge at /labs/python. Fix the broken program, run it yourself, then use check to prove the real end state.