Sequence Patterns and Mutability

Scenario: Changing a nested list unexpectedly changes another variable that points to it.

New words, in plain English

• Reference - a connection from a name to an object
• Shallow copy - a new outer collection that still shares nested objects
• Sequence - an ordered value supporting indexes

Assignment does not copy a list; both names point to one object. enumerate supplies index-value pairs, zip walks collections together, and membership checks use in.

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

names = ["api", "db"]
for number, name in enumerate(names, start=1):
    print(number, name)
ports = dict(zip(names, [80, 5432]))

Tip: When nested independence matters, learn copy.deepcopy, but prefer simple immutable shapes when possible.

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