>>> Python for Beginners Chapter 07 of 10

Chapter 07 · Repeating

Repeating With Loops

Computers are brilliant at doing boring things many times without complaint. Loops are how you tell them to repeat — the moment programming starts to feel powerful.

The for loop — repeat a set number of times

range(n) counts from 0 up to (not including) n. A for loop walks through it:

for number in range(5):
    print(f"This is line {number}")
This is line 0 This is line 1 This is line 2 This is line 3 This is line 4

Each time round, number holds the next value. The indented block runs once per value.

Counting from 1

range(1, 6) goes from 1 up to (not including) 6:

total = 0
for n in range(1, 6):
    total = total + n
print(f"1+2+3+4+5 = {total}")
1+2+3+4+5 = 15

The while loop — repeat until something changes

A while loop keeps going as long as its condition stays true:

count = 3
while count > 0:
    print(f"{count}...")
    count = count - 1
print("Lift off!")
3... 2... 1... Lift off!

Looping over text

You can loop straight over a string, one character at a time:

for letter in "Zambia":
    print(letter)
Z a m b i a
✍️ Try it yourself

Use a for loop to print the 7 times table (7, 14, 21 ... up to 70). Hint: for n in range(1, 11): print(n * 7).

Beware the endless loop

In a while loop, something inside must eventually make the condition false — otherwise it runs forever. In the countdown above, count = count - 1 is what saves us. Forget it and the program never stops.

Recap