Loops
📚 What are loops? Loops are commands that **repeat** work automatically so you do not type the same lines again and again. A `for` loop is great when you know how many steps you want (or you want to walk through a list). A `while` loop keeps going **as long as** a condition stays true.
Appy Says…
Without loops, you'd need to copy-paste the same code hundreds of times. With loops, you write it once and the computer repeats it as many times as you need. Games, animations, data processing — everything uses loops.
What are Loops?
A loop repeats a block of code automatically. Python has two kinds: for loops (repeat a specific number of times or go through every item in a list) and while loops (keep repeating until a condition becomes False).
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for i in range(5):runs the block 5 times (i = 0, 1, 2, 3, 4) - •
for item in my_list:runs the block once for every item in the list - •
while condition:keeps running as long as the condition is True - •
breakexits the loop early;continueskips to the next round
Think of it like spawning enemies in a game
In a wave-based game, the engine loops through each enemy in the wave and spawns it: for each enemy in wave: spawn(enemy). When all enemies are dead, the condition changes and the loop stops. A while loop is like a game lobby — it keeps checking 'are all players ready?' and only moves on when they are.
How For Loops Work
- •range(n) generates numbers from 0 up to (but not including) n
- •range(start, stop) generates from start up to stop
- •range(start, stop, step) goes in steps:
range(0, 10, 2)gives 0, 2, 4, 6, 8 - •The loop variable (
i) changes each round — you can use it inside the loop - •To iterate a list:
for fruit in fruits:—fruitbecomes each item in turn
Real-World Examples
- •Sending a notification to every follower:
for user in followers: send_notification(user) - •Animating 60 frames per second: the game loop runs 60 times every second
- •Checking every product in a shop:
for item in cart: total += item.price - •Loading a playlist:
for song in playlist: add_to_queue(song) - •A quiz app:
for question in questions: ask(question)
Key Facts
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range()does NOT include the end number —range(5)is 0,1,2,3,4 - •An infinite loop (
while True:) runs forever — you need abreakinside to exit - •Loops can be nested inside other loops (a loop inside a loop — like a grid)
- •
len(my_list)gives the number of items — useful in range:range(len(items)) - •Most professional code uses loops thousands of times — they're everywhere
Watch Out: Infinite Loops
A while loop that never becomes False will run forever and freeze your program. Always make sure your loop condition can eventually become False, or include a break statement.
Remember
Use for when you know the count or have a list to go through. Use while when you're waiting for something to change (user input, a sensor value, a timer). If you're not sure, start with for.
What You Learned
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for i in range(n):— repeats n times - •
for item in list:— goes through every item in a list - •
while condition:— repeats until condition is False - •
breakexits early;continueskips to the next round - •Loops are one of the most-used features in all programming
Key Facts
- →
range()does NOT include the end number —range(5)is 0,1,2,3,4 - →An infinite loop (
while True:) runs forever — you need abreakinside to exit - →Loops can be nested inside other loops (a loop inside a loop — like a grid)
- →
len(my_list)gives the number of items — useful in range:range(len(items)) - →Most professional code uses loops thousands of times — they're everywhere
Real-World Examples
Remember
Use for when you know the count or have a list to go through. Use while when you're waiting for something to change (user input, a sensor value, a timer). If you're not sure, start with for.
Quick Quiz
How many times does range(3) run?