For Loops, Doing Things Repeatedly

Stop copying and pasting, let loops do the repetitive work for you

Imagine you had to print the numbers 1 to 1000. You're not going to write 1000 print() statements. That's what loops are for, repeat an action many times without repeating your code.

How would you approach this? Think first, then expand.

For loop basicspython

# Loop through a range of numbers
for i in range(5):
    print(i)
# prints: 0, 1, 2, 3, 4

# range(start, stop)
for i in range(1, 6):
    print(i)
# prints: 1, 2, 3, 4, 5

🔍Code TracerStep 1 / 9

trace.py

1fruits = ["apple", "banana", "cherry"]←

2for fruit in fruits:

3 print(fruit)

Variables

No variables yet

Step 1 / 9

Loop through a listpython

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)
# prints: apple, banana, cherry

`range(n)` generates numbers from 0 to n-1. `range(start, stop)` generates from start up to (not including) stop. `range(start, stop, step)`, step controls the increment.

Accumulator pattern, building a result in a looppython

# Sum all numbers from 1 to 10
total = 0
for i in range(1, 11):
    total += i   # same as: total = total + i
print(total)     # 55

The accumulator pattern (start with 0, add to it in a loop) solves dozens of problems: sum, count, build a string, find max/min, etc.

🌍In the Real World...

Iterating over a list of servers to check health. Looping through pod names to find crashed ones. Processing each line in a log file. This pattern is the backbone of DevOps scripting.

Practice Exercises

0/3 solved

Exercise 1 of 3easy

⏱ 00:00

Sum 1 to N

Write a function sum_to_n(n) that returns the sum of all integers from 1 to n (inclusive).
Example: sum_to_n(5) → 15 (1+2+3+4+5)

solution.py

1 / 3

Exercise 2 of 3easy

⏱ 00:00

Multiplication Table

Write a function times_table(n) that prints the multiplication table for n, from 1 to 10.
Example output for times_table(3):`3 x 1 = 33 x 2 = 6...3 x 10 = 30`

solution.py

2 / 3

Exercise 3 of 3easy

⏱ 00:00

Only Even Numbers

Write a function filter_evens(numbers) that returns a new list containing only the even numbers from the input list.
Example: filter_evens([1,2,3,4,5,6]) → [2,4,6]

solution.py

3 / 3

Solve all 3 exercises to unlock completion

Previous Next