FOR ... TO as range() in Python

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Quick Questions

Shade in the A or B circle for each question.

1. Which Python loop matches FOR i ← 1 TO 10?

A for i in range(1, 10):

B for i in range(1, 11):

2. How many times does for i in range(1, 6): run the loop body?

A 5 times (i is 1, 2, 3, 4, 5)

B 6 times (i is 1, 2, 3, 4, 5, 6)

3. Which statement about range(1, n) is correct?

A i stops at n - 1

B i stops at n

4. Which Python loop matches FOR Count ← 0 TO 20 STEP 5?

A for count in range(0, 20, 5):

B for count in range(0, 21, 5):

5. In range(2, 11, 3), what is the third argument 3?

A The STEP: how much i changes each time

B The end value: where the loop stops

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1for i in range(1, n + 1):		AOff-by-one error: range(1, 10) stops at 9, so the loop misses the value 10.
2for i in range(10, 0, -2):		Bfor num in range(0, 21, 5):
3The pseudocode FOR Count ← 1 TO 5 runs for the values 1, 2, 3, 4 and 5		CPython version of FOR i ← 1 TO n; the + 1 makes the loop include n
4The pseudocode FOR Num ← 0 TO 20 STEP 5 becomes range() with a third argument for the STEP		Dfor count in range(1, 6):
5for i in range(1, 10): # FOR i ← 1 TO 10		EThe end value 1 is not included when counting down, so the loop stops at 2 and misses 1.
6for i in range(5, 1, -1): # FOR i ← 5 TO 1 STEP -1		FCounts down 10, 8, 6, 4, 2 in steps of 2 and stops before reaching 0

Definitions

for i in range(1, n + 1):

Fill in the Blanks

Complete each line of code by filling in the missing parts.

# FOR i <- 1 TO n for i in range(1, _____): print(i)

# FOR i <- 1 TO 5 for i in range(1, _): print(i)

# FOR i <- 0 TO 20 STEP 5 for i in range(0, 21, _): print(i)

# FOR i <- 5 TO 1 STEP -1 for i in range(5, _, -1): print(i)

# FOR i <- 10 TO 2 STEP -2 for i in range(10, 1, __): print(i)

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A n = 5

B total = 0

C for i in range(1, n):

D total = total + i

E print(total)

Question 2

A n = 5

B print("Countdown")

C print("Start")

D for i in range(n, 1, -1):

E print(i)

Question 3

A total = 0

B for i in range(2, 10, 2):

C total = total + i

D print("Sum 2 to 10:", total)

Question 4

A for i in range(1, 12):

B print(3 * i)

C print("3 times table to 12")

Question 5

A start = 10

B print("Countdown")

C for i in range(start, 0, 1):

D print(i)

E print("Go!")

Answer Key

FOR ... TO as range() in Python

Section A: Quick Questions

B — for i in range(1, 11):

A — 5 times (i is 1, 2, 3, 4, 5)

A — i stops at n - 1

B — for count in range(0, 21, 5):

A — The STEP: how much i changes each time

Section B: Match the Pairs

for i in range(1, n + 1): → Python version of FOR i ← 1 TO n; the + 1 makes the loop include n

for i in range(10, 0, -2): → Counts down 10, 8, 6, 4, 2 in steps of 2 and stops before reaching 0

The pseudocode FOR Count ← 1 TO 5 runs for the values 1, 2, 3, 4 and 5 → for count in range(1, 6):

The pseudocode FOR Num ← 0 TO 20 STEP 5 becomes range() with a third argument for the STEP → for num in range(0, 21, 5):

for i in range(1, 10): # FOR i ← 1 TO 10 → Off-by-one error: range(1, 10) stops at 9, so the loop misses the value 10.

for i in range(5, 1, -1): # FOR i ← 5 TO 1 STEP -1 → The end value 1 is not included when counting down, so the loop stops at 2 and misses 1.

Section C: Definitions

for i in range(1, n + 1): — Python for FOR i ← 1 TO n. range() stops before its end value, so use n + 1 to include n. A third argument is the STEP; a negative step counts down.

Section D: Fill in the Blanks

# FOR i <- 1 TO n
for i in range(1, n + 1):
    print(i)

# FOR i <- 1 TO 5
for i in range(1, 6):
    print(i)

# FOR i <- 0 TO 20 STEP 5
for i in range(0, 21, 5):
    print(i)

# FOR i <- 5 TO 1 STEP -1
for i in range(5, 0, -1):
    print(i)

# FOR i <- 10 TO 2 STEP -2
for i in range(10, 1, -2):
    print(i)

Section E: Spot the Error

C — range() stops before its end value, so range(1, n) only goes up to 4 and misses 5. To match FOR i <- 1 TO n it must be range(1, n + 1).

D — When counting down, range() stops before its end value, so an end of 1 stops at 2 and never prints 1. To count down to 1 the end value must be 0: range(n, 0, -1).

B — FOR i <- 2 TO 10 STEP 2 includes 10, but range() stops before its end value, so range(2, 10, 2) misses 10. The end value must be 11: range(2, 11, 2).

A — The table should run from 1 to 12, but range(1, 12) stops at 11. Add 1 to the end value: range(1, 13).

C — To count down, the step (third argument) must be negative. A step of 1 counts upwards from 10, so the loop never runs. It should be range(start, 0, -1).