Step: String methods: split, strip, join

.split(",") breaks a string into a list on a separator; .strip() trims surrounding whitespace; ", ".join(list) glues a list back into one string.

Why it matters: this split → clean → join pattern is the bread-and-butter of parsing messy text input.

Example: "a, b".split(",") is ["a", " b"]; " b".strip() is "b".

Your turn: split line on commas, strip each piece, then rejoin with ", ".

Pitfall: ", ".join(...) needs a list of strings — joining a list containing numbers raises TypeError.