Commenting out code to isolate a bug

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. A line of Python starts with # in front of it. What happens when the program runs?

A Python runs the line and prints a warning

B Python skips the line, so it is temporarily disabled

2. Your program crashes and you suspect the line total = price / qty. Which approach isolates the bug?

A # total = price / qty

B del total = price / qty

3. Why comment out a line instead of deleting it while hunting for a bug?

A You can restore it later by removing the #

B Python fixes commented-out lines automatically

4. You want to disable a block of five lines at once. What is the quickest method in most editors?

A Select the block and use the editor's comment shortcut

B Type # once at the top of the block only

5. Which block is fully commented out?

A # x = 5 y = x * 2 print(y)

B # x = 5 # y = x * 2 # print(y)

Match the Pairs

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

Left column		Right column
1# total = total + price		AA block of lines commented out one by one, so none of them run while the bug is being isolated.
2# print(average) # print(count)		BThis line is commented out, so Python skips it and does not add the price to the total.
3Restore disabled code after testing by removing the # from the front of the line.		Ctotal = total + price
4Comment out the suspect line to see if the bug disappears when that line does not run.		DThe # is placed after the code, so the line still runs. The # must go at the start of the line to disable it.
5total = total + price # print(total)		EOnly the for line is commented out, leaving an indented line that causes an IndentationError. Comment out the whole block.
6# for item in prices: total = total + item		F# result = 10 / count

Definitions

# (commenting out)

Fill in the Blanks

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

_ print(total / count)

_ for n in nums: # total += n print(len(nums))

total = 10 count = 2 _____(total / count)

name = "Sam" _ age = int("twelve") print(name)

if score > 50: _ print("Pass") print("Done")

Spot the Error

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

Question 1

A scores = [8, 9, 7]

B total = sum(scores)

C // average = total / 0

D print(total)

Question 2

A x = 10

B y = x / 0 #

C print(x)

Question 3

A count = 3

B # for i in range(count):

C # print(i / 0)

D count -= 1

E print(count)

Question 4

A # bug fixed: code restored

B total = 0

C total += 5

D # print(total)

Question 5

A age = int(input('Age: '))

B /* print(age + '1') */

C print('Done')

Answer Key

Commenting out code to isolate a bug

Section A: Quick Questions

B — Python skips the line, so it is temporarily disabled

A — # total = price / qty

A — You can restore it later by removing the #

A — Select the block and use the editor's comment shortcut

B — # x = 5 # y = x * 2 # print(y)

Section B: Match the Pairs

# total = total + price → This line is commented out, so Python skips it and does not add the price to the total.

# print(average) # print(count) → A block of lines commented out one by one, so none of them run while the bug is being isolated.

Restore disabled code after testing by removing the # from the front of the line. → total = total + price

Comment out the suspect line to see if the bug disappears when that line does not run. → # result = 10 / count

total = total + price # print(total) → The # is placed after the code, so the line still runs. The # must go at the start of the line to disable it.

# for item in prices: total = total + item → Only the for line is commented out, leaving an indented line that causes an IndentationError. Comment out the whole block.

Section C: Definitions

# (commenting out) — Putting # in front of a line, or a selected block, stops Python running it. Use this to isolate a bug, then remove the # to restore the code.

Section D: Fill in the Blanks

# print(total / count)

# for n in nums:
#     total += n
print(len(nums))

total = 10
count = 2
print(total / count)

name = "Sam"
# age = int("twelve")
print(name)

if score > 50:
    # print("Pass")
    print("Done")

Section E: Spot the Error

C — // is not a Python comment, so Python tries to run it and raises a SyntaxError. To disable the suspect line, put # at the start: # average = total / 0.

B — A # only disables the text after it. Here the code comes first, so y = x / 0 still runs and causes a ZeroDivisionError. Put the # at the start of the line instead.

D — When commenting out a block, every line of it needs a #. This indented line was left active, but its for header is a comment, so Python raises an IndentationError. It should be: # count -= 1.

D — After isolating the bug, the # must be removed to restore the code. With the # still there, print(total) never runs and nothing is shown. It should be print(total).

B — /* */ is a comment style from other languages, not Python. Python would raise a SyntaxError. Use # at the start: # print(age + '1').