Defaults, Keywords, *args, and **kwargs

Scenario: A logger needs a sensible default but also optional extra labels.

New words, in plain English

• Default argument - a parameter value used when none is supplied
• Keyword argument - an argument supplied by parameter name
• *args - extra positional arguments collected in a tuple
• **kwargs - extra named arguments collected in a dict

Required parameters come before defaults. Keyword calls improve clarity. Use variadic arguments when the API truly accepts a flexible number, not to hide an unclear design.

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

def log(message, level="INFO", *tags, **fields):
    print(level, message, tags, fields)
log("ready", "INFO", "api", host="edge-01")

Tip: Never use a mutable list or dict as a default; use None and create it inside.

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