Count-controlled iteration: for loops and range()

for with range() (spec 7.1.1)

range(stop) gives 0 up to stop - 1. range(start, stop) starts at start. range(start, stop, step) counts in steps. The stop value is never included.

for i in range(3):
    print(i, end=" ")
print()
for i in range(2, 11, 4):
    print(i, end=" ")
print()
for i in range(5, 0, -1):
    print(i, end=" ")

Output:

0 1 2 
2 6 10 
5 4 3 2 1 

Looping over a structure

A for loop can visit every item of a list, string, tuple, set or dictionary directly. To get the index as well, loop over range(len(items)).

names = ["Ana", "Ben", "Cai"]
for name in names:
    print(name.upper())
for i in range(len(names)):
    print(i, names[i])

Output:

ANA
BEN
CAI
0 Ana
1 Ben
2 Cai

Running totals and counts

Initialise before the loop, update inside it, use the result after it:

marks = [12, 18, 9, 15]
total = 0
count = 0
for m in marks:
    total = total + m
    if m >= 12:
        count = count + 1
print(total, count)

Output:

54 3

Nested loops

A loop inside a loop runs the inner loop completely for each pass of the outer loop. Two nested loops over n items do n x n passes, which matters for efficiency.

for row in range(1, 4):
    line = ""
    for col in range(1, 4):
        line = line + str(row * col) + " "
    print(line)

Output:

1 2 3 
2 4 6 
3 6 9 

Worked example

How many times does the body of for i in range(3, 20, 4) run, and what values does i take?

1. Start at 3 and add 4 each time while i < 20.
2. Values: 3, 7, 11, 15, 19
3. Count them: 5

Answer: 5 times

Check yourself

1. What is displayed when this code runs? ```python for i in range(1, 6, 2): print(i, end=" ") ```
   Show answer

   1 3 5 . range(1, 6, 2) gives 1, 3, 5 (6 is excluded), so 1 3 5.

2. What is the value of total after this code runs? ```python total = 0 for k in range(1, 5): total = total + k * k ```
   Show answer

   30. 1 + 4 + 9 + 16 = 30. range(1, 5) stops at 4.

3. How many times is print called by this code? ```python for a in range(4): for b in range(3): print(a, b) ```
   Show answer

   12. The inner loop runs 3 times for each of the 4 outer passes: 4 x 3 = 12.

4. What is displayed when this code runs? ```python for i in range(10, 0, -3): print(i, end=" ") ```
   Show answer

   10 7 4 1 . Counting down in steps of 3 from 10, stopping before 0: 10 7 4 1.

5. What is displayed when this code runs? ```python count = 0 for ch in "programming": if ch == "m": count = count + 1 print(count) ```
   Show answer

   2. A for loop over a string visits each character; 'm' appears 2 times.

6. This code should print the numbers 1 to 10 inclusive. Which line completes it? ```python __________ print(n, end=" ") ```
   • `for n in range(1, 11):`
   • `for n in range(1, 10):`
   • `for n in range(10):`
   • `for n in range(0, 11):`
   Show answer

   `for n in range(1, 11):`. The stop value is excluded, so range(1, 11) gives 1 to 10.

7. This code should display 12 but it does not. Which line number is in the wrong place? ``` 1 nums = [4, 7, 1] 2 for n in nums: 3 total = 0 4 total = total + n 5 print(total) ```
   Show answer

   3. total = 0 is inside the loop (line 3), so it is reset on every pass and only the last value survives. Initialise the total once, before the loop.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Computer Science specification (XCP01/YCP01), first teaching 2026
• Pearson IAL Computer Science Unit 2 Programming Language Subset (PLS), Python 3
• Pearson IAL Computer Science IAS sample assessment materials (Unit 2 paper and mark scheme)

Last updated 8 November 2026. Spotted a mistake? Tell us.