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05LOOPS · FOR

Repeat without rewriting.

A loop repeats one small job and knows when to stop.

LOOK FIRST

Loops are useful for patterns.

Choose one small job

Blink a light, draw a star, or say “beep.” Keep the repeated job tiny.

3×

Choose how many times

range(3) gives the loop three turns.

■

Then stop

A good beginner loop has a clear ending. It does not spin forever.

for turn in range(3):beepbeepbeepdone!

STEP BY STEP

Watch the loop work.

A loop has a box that changes on every turn.

for turn in range(3):turn is a box. range(3) fills it with 0, then 1, then 2.

print(turn)The indented line repeats. It shows what is in the box now.

print("done")Not indented, so it runs once, after the loop ends.

snacks = ["apple", "pear", "grape"]A list box, like in Boxes of all kinds. It has 3 spaces.

for snack in snacks:snack takes each item of the list, one turn at a time.

print("I like", snack)Repeats 3 times, once for each item: apple, pear, grape.

print(turn)012done!

range starts at 0

Computers start counting at 0. range(3) gives 0, 1, 2. That is still three turns.

The loop box changes

The word after for is a box. It gets a new value on every turn.

Indented lines repeat

Lines pushed right repeat on every turn. Lines on the left run once.

KEEP A COUNT

A loop can add up as it goes.

stars = 0Start with an empty count: 0 stars.

for turn in range(4):Four turns.

stars = stars + 1Each turn, take what is in the box and add 1: 1, 2, 3, 4.

print(stars)Runs once at the end and shows 4.

RUN IT

Help PyBot beep in a pattern.

Guess first. Then run real Python and check.

Guess the result

for turn in range(3):
    print("beep")

How many times will PyBot beep?

beep.pyREAL PYTHON

OUTPUT

Ready. Press Run Python.

Python runs here thanks to Pyodide ♥

Pyodide 314.0.3 runs CPython in your browser with WebAssembly.

Open-source under the Mozilla Public License 2.0. License

Now change one thing: Change 3 to another small number, like 5. Run again and count the beeps.

YOUR TURN

Count what repeats.

Try each tiny question. A wrong answer becomes something to review.

0Completed

9Not tried

0Review

Three turns

for turn in range(3):
  print("beep")

How many beeps appear?

Find the repeated job

for star in range(2):
  print("★")

What does the loop repeat?

Know when it stops

for light in range(4):
  print("light")

When is the loop finished?

The first turn

for turn in range(3):
    print(turn)

Which number shows first?

One turn per item

colors = ["red", "blue"]
for color in colors:
    print(color)

How many turns does the loop take?

Outside the loop

for turn in range(5):
    print("hop")
print("rest")

How many times does the last word show?

Keep a count

stars = 0
for turn in range(3):
    stars = stars + 2
print(stars)

What does Python show?

Fix PyBot's code

The step to repeat must be inside the loop. Move it in with spaces.

PyBot's code

Goal output

Beep
Beep
Beep