Python for and while loops: repeat with a reason

The idea

If you have three clues, you could write three almost-identical print lines. A loop separates the collection from the instruction to perform on each item. That makes the idea easier to extend: a fourth clue does not require a fourth copy of the instruction. Follow the loop one pass at a time, writing down which value the loop variable currently holds.

A tiny experiment

clues = ["key", "receipt", "map"]
for clue in clues:
    print("Inspect: " + clue)
print("All checked.")

Inspect: key
Inspect: receipt
Inspect: map
All checked.

Read it one step at a time

1. Square brackets create a list. Here the entries are strings.
2. for gives clue each list item in turn. The indented instruction runs once for each item.
3. The final print is outside the loop, so it runs once after all three passes. range(3) can instead supply 0, 1 and 2.

Make one change

Move the last print inside the loop by adding four spaces. How many times will it appear?

Keep following the trail

• Activity 02: Read the backwards note
• Activity 06: Find the prime locker
• Activity 08: Choose the allowed commands

Sources & further reading

• Python control flow

Companion notes for Coding Adventure by James Colby. Historical claims link to their sources; the examples are written for this learning trail.