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for Loops and range()

Python 3.14 · ✓ verified by execution on 2026-07-22

The for loop in Python iterates over the items of any sequence.

python 
words = ['cat', 'window', 'defenestrate']
for w in words:
    print(w)
Output 
cat
window
defenestrate

The range() Function

If you do need to iterate over a sequence of numbers, the built-in function, range() is the tool you need.

python 
for i in range(3):
    print(i)
Output 
0
1
2

Remember: The given end point is never part of the generated sequence. Thus, range(3) yields 0, 1, 2 but not 3.

Start, Stop, and Step

You can also choose where to start and how big each step is. The full form is range(start, stop, step) — start counting at start, stop before stop, and jump by step each time.

python 
for i in range(2, 8, 2):
    print(i)
Output 
2
4
6
start = 2 · step = 2 · stop = 8 (excluded) 0 1 2 3 4 5 6 7 8
range(2, 8, 2) starts at 2, counts by 2, and stops before 8 — so 8 is never produced.

Try It Yourself

Drag the slider to change how many rows this loop prints, then press Run. Notice that range(n) always starts at 0, so n is exactly how many times the loop body runs.

python
drag to change the value, then Run 
n = 5
for i in range(n):
    print('*' * (i + 1))
Output 
*
**
***
****
*****

Counting Backwards

You can even use a negative step to count backwards:

python 
for i in range(0, -3, -1):
    print(i)
Output 
0
-1
-2

Iterating with Indices

If you need both the index and the item, you can iterate over the indices of a sequence:

python 
a = ['Mary', 'had', 'a', 'little', 'lamb']
for i in range(len(a)):
    print(i, a[i])
Output 
0 Mary
1 had
2 a
3 little
4 lamb

Common Misconceptions

A for loop in Python is like C where you define the initialization, condition, and increment. Python’s for loop iterates over the items of any sequence in the order they appear.

range(5) generates numbers from 1 to 5. range(5) generates numbers from 0 to 4 (the end point is exclusive).

Reading that and agreeing with it is easy. Predicting it under your own steam is the part that sticks — so before you scroll, commit to an answer:

Predict the output python

Three loops, three ranges. Write down every line this prints, in order — and be careful with the third one.

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

for i in range(3, 6):
    print(i)

for i in range(6, 3):
    print("never runs")
Output 
0
1
2
3
4
5

If you wrote 1 2 3 for the first loop, or expected the third loop to count downwards, you have just found the exact edge of what you knew — which is worth more than getting it right.

Edge Cases

Under the Hood

Watch how the for loop dynamically assigns the next value from range() to the iteration variable on each cycle:

python · visualize 
for i in range(2, 8, 2):
    print("Value:", i)
print("Loop finished")

Check yourself

What numbers will `range(3)` generate?

Reveal answer

0, 1, 2 — range(stop) starts at 0 by default and ends before the stop value, making the end point exclusive.

How does Python's `for` loop differ from traditional C-style for loops?

Reveal answer

It directly iterates over the items of a sequence, rather than just counting numbers. — Python's for loop iterates over the items of any iterable (like a list or string) in the order they appear.

What does `range(2, 8, 2)` generate?

Reveal answer

2, 4, 6 — It starts at 2, increments by 2 (the step), and stops before it reaches 8.

Challenges

Challenge 1 +50 XP

Use a for loop and the `range()` function to print the numbers 1 through 5 (inclusive).

python
  • Test 1 — expects "1\n2\n3\n4\n5"
Need a hint? (−25% XP)

Use range(1, 6) since the stop value is exclusive.

Show solution (0 XP) 
for i in range(1, 6):
    print(i)

Challenge 2 +100 XP

Iterate over the list `colors` and print each item.

python
  • Test 1 — expects "red\ngreen\nblue"
Need a hint? (−25% XP)

Use `for color in colors:`.

Show solution (0 XP) 
colors = ['red', 'green', 'blue']
for color in colors:
    print(color)

🐞 Bug Hunt +75 XP

This code should print every colour in order. It runs without an error — and prints the wrong thing. Find the defect and fix it.

This code runs. It just does the wrong thing. Read it, find the defect, fix it — the tests below decide when you are right.

python
  • Test 1 — expects "red\ngreen\nblue"
Need a hint? (−25% XP)

Negative indexes are legal in Python — they count from the end. What is colors[-1]?

Show solution (0 XP) 
colors = ['red', 'green', 'blue']
for i in range(len(colors)):
    print(colors[i])