Lesson 4 of 7
Loops
Automate repetitive tasks and write efficient code using Python for and while loops.
Learn it
If you had to write a message 100 times on a chalkboard, your hand would get exhausted! Programmers are clever: they use loops to repeat code automatically.
Python has two main kinds of loops: for loops (great when you know how many times you want to repeat) and while loops (great when you want to repeat until something changes).
Key terms
- Loop
- A control structure that repeats a block of code multiple times.
- Iteration
- A single pass or repetition through a block of looped instructions.
- For Loop
- A loop designed to repeat instructions a predetermined number of times or over a sequence.
- While Loop
- A loop that continues executing as long as a specified condition remains true.
Inside a Loop Cycle
See how a countdown loop evaluates and repeats until its exit condition is met.
- 1Initialisation: A counter variable is set to a starting number, for instance timer = 3.
- 2Condition Check: Python evaluates whether timer > 0 is True.
- 3Body Execution: The indented block runs, printing the current timer count to the player.
- 4Decrement & Repeat: The timer decreases by 1 and execution loops back to the condition check.
Printing Repetitive Actions with Loops
pythonprint("Starting laser charge:")
for i in range(1, 4):
print("Charging power level:", i)
print("Lasers fully charged!")The for loop uses range(1, 4) to run the indented print line three times, with i taking values 1, 2, and 3.
Try it
Predict the final number outputted by this Python code:
pythontotal = 0
for i in range(3):
total = total + 2
print(total)Challenge
Write a for loop in Python that prints the numbers 5, 4, 3, 2, 1 followed by Blast off!
Pick whichever way suits you — every mode earns the same bonus XP.
Write at least 40 more characters to submit.
Mark your own work
Guided walkthrough — 0/5 clues revealed
- Clue 1 locked — reveal it only if you get stuck.
- Clue 2 locked — reveal it only if you get stuck.
- Clue 3 locked — reveal it only if you get stuck.
- Clue 4 locked — reveal it only if you get stuck.
- Clue 5 locked — reveal it only if you get stuck.
Each clue costs 4 XP (never below 20 XP). You'd earn 40 XP right now.
Extension: Rewrite the countdown using a while loop that decreases a rocket_timer variable.