Debugging with print()

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Quick Questions

Shade in the A or B circle for each question.

1. Your program gives the wrong total. What is a good first debugging step using print()?

A Delete the variable total and start again

B Add print("total =", total) to see the value as the program runs

2. Which line is a helpful debug print?

A print("score =", score)

B print("here")

3. Why do we put a label like "total =" inside a debug print?

A So you can tell which value is being shown in the output

B Because Python will crash without a label

4. A while loop adds numbers to total but the answer is wrong. Where should you put the debug print to watch total change?

A Inside the loop, indented under the while line

B Before the loop starts, at the very top

5. Your for loop has this debug print inside it: print("i =", i). What will it show?

A The value of i only once, after the loop ends

B The value of i each time the loop repeats

Match the Pairs

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

Left column		Right column
1print("total =", total)		Atotal = total + price print("total =", total)
2print("i =", i, "score =", score)		B# print("total =", total)
3Show the value of a variable after a calculation to check it is correct		CThe debug print is not indented, so it runs only once after the loop and does not show score changing each time. Fix: indent it inside the loop.
4Once the bug is fixed, remove the debug print or turn it into a comment so the output stays clean		DA debug print inside a loop that shows how i and score change on each pass
5print("total = total")		EA debug print that shows the current value of the variable total while the program runs
6for i in range(5): score = score + i print("score =", score)		FThe variable is inside the quotes, so it prints the words 'total = total' instead of the value. Fix: print("total =", total)

Definitions

print("total =", total)

Fill in the Blanks

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

total = 0 total = total + 5 print("total =", _____)

for i in range(3): total = total + i _____("total =", total)

for num in scores: total = total + num print("num =", ___)

total = total + price _ print("total =", total) print(total)

_____ count < 3: print("count =", count) count = count + 1

Spot the Error

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

Question 1

A total = 0

B for n in range(1, 4):

C total = total + n

D print("total =" total)

E print("final", total)

Question 2

A count = 0

B while count < 3:

C print("count =", Count)

D count = count + 1

Question 3

A price = 5

B qty = 3

C print("qty =", qty

D cost = price * qty

Question 4

A total = 0

B for n in [2, 4, 6]

C total = total + n

D print("total =", total)

Question 5

A score == 10

B score = score + 5

C print("score =", score)

Answer Key

Debugging with print()

Section A: Quick Questions

B — Add print("total =", total) to see the value as the program runs

A — print("score =", score)

A — So you can tell which value is being shown in the output

A — Inside the loop, indented under the while line

B — The value of i each time the loop repeats

Section B: Match the Pairs

print("total =", total) → A debug print that shows the current value of the variable total while the program runs

print("i =", i, "score =", score) → A debug print inside a loop that shows how i and score change on each pass

Show the value of a variable after a calculation to check it is correct → total = total + price print("total =", total)

Once the bug is fixed, remove the debug print or turn it into a comment so the output stays clean → # print("total =", total)

print("total = total") → The variable is inside the quotes, so it prints the words 'total = total' instead of the value. Fix: print("total =", total)

for i in range(5): score = score + i print("score =", score) → The debug print is not indented, so it runs only once after the loop and does not show score changing each time. Fix: indent it inside the loop.

Section C: Definitions

print("total =", total) — A debug print. Add a line like this to show a variable's value while the program runs, so you can spot where it goes wrong. Put one inside a loop to watch it change, then remove it once fixed.

Section D: Fill in the Blanks

total = 0
total = total + 5
print("total =", total)

for i in range(3):
    total = total + i
    print("total =", total)

for num in scores:
    total = total + num
    print("num =", num)

total = total + price
# print("total =", total)
print(total)

while count < 3:
    print("count =", count)
    count = count + 1

Section E: Spot the Error

D — There is a comma missing between the label and the variable. The debug print must be print("total =", total) so Python knows they are two separate things to show.

C — Python cares about capital letters. The variable is called count, not Count, so the debug print causes a NameError. It should be print("count =", count).

C — The closing bracket is missing, which is a syntax error. The debug print should end with a bracket: print("qty =", qty).

B — A for loop line must end with a colon. Without it the program will not run, so you cannot even see the debug print inside the loop. It should be for n in [2, 4, 6]:

A — A single = stores a value in a variable, but == compares two values. Using == means score is never created, so the debug print would fail. It should be score = 10.