Dependability of a program
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Which program is more dependable?
2. True or false: A program that works with perfect input every time is automatically dependable.
3. A user enters -5 for their age. Which response shows a dependable program?
4. Which code is better for dependability?
5. What does error handling help a program do?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1try: age = int(input()) except ValueError: print('Enter a number') | AKeeps asking until the input is valid, so bad data never gets used | |
| 2while age < 0 or age > 120: age = int(input('Age: ')) | BTyping letters such as 'abc' causes a ValueError and crashes the program, because there is no error handling. | |
| 3Reliability: the program gives the right result every time it is run with valid input | Cdef add(a, b): return a + b | |
| 4Handling invalid input: check the input before using it | DCatches bad input so the program shows a message instead of crashing | |
| 5age = int(input('Age: ')) print(age + 1) | Eif not name.isdigit(): print('Numbers only') | |
| 6try: n = int(input()) except: pass | FThe error is silently ignored, so n is never set and the program fails later without telling the user what went wrong. |
C
Definitions
dependability
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
___:
n = int(input("Number: "))
except ValueError:
2.
try:
n = int(input("Number: "))
except __________:
3.
age = int(input("Age: "))
while age _ 0:
age = int(input("Age: "))
4.
if count __ 0:
print(total / count)
5.
except ValueError:
_____("Please enter a number")
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
try:
B
age = int(input('Age: '))
C
catch ValueError:
D
print('Enter a number')
Question 2
A
while True:
B
n = int(input('Number: '))
C
if n.isdigit():
D
break
E
print(int(n))
Question 3
A
def safe_div(a, b):
B
if b == 0:
C
return a / b
D
return a / b
Question 4
A
try
B
f = open('data.txt')
C
except FileNotFoundError:
D
print('File missing')
Question 5
A
score = input('Score: ')
B
if score.isdigit():
C
print('Invalid score')
D
else:
E
print('Saved')
Answer Key
Dependability of a program
Section A: Quick Questions
Q1
B — One that gives a clear message when a user types letters instead of a number
Q2
A — False
Q3
A — Show an error message and ask for the age again
Q4
A — try:
n = int(input())
except ValueError:
print('Numbers only')
Q5
B — Keep running or fail safely when something goes wrong
Section B: Match the Pairs
Q1
try:
age = int(input())
except ValueError:
print('Enter a number') → Catches bad input so the program shows a message instead of crashing
Q2
while age < 0 or age > 120:
age = int(input('Age: ')) → Keeps asking until the input is valid, so bad data never gets used
Q3
Reliability: the program gives the right result every time it is run with valid input → def add(a, b):
return a + b
Q4
Handling invalid input: check the input before using it → if not name.isdigit():
print('Numbers only')
Q5
age = int(input('Age: '))
print(age + 1) → Typing letters such as 'abc' causes a ValueError and crashes the program, because there is no error handling.
Q6
try:
n = int(input())
except:
pass → The error is silently ignored, so n is never set and the program fails later without telling the user what went wrong.
Section C: Definitions
Q1
dependability — A dependable program works correctly and reliably every time, even when users enter unexpected or invalid input, because it handles errors instead of crashing.Section D: Fill in the Blanks
Q1
try:
n = int(input("Number: "))
except ValueError:Q2
try:
n = int(input("Number: "))
except ValueError:Q3
age = int(input("Age: "))
while age < 0:
age = int(input("Age: "))Q4
if count != 0:
print(total / count)Q5
except ValueError:
print("Please enter a number")Section E: Spot the Error
Q1
C — Python does not use catch. The error handler must be written as 'except ValueError:' so invalid input is handled instead of crashing.
Q2
B — Converting with int() before checking crashes the program if the user types letters. Keep the input as text, check it with isdigit(), and convert afterwards.
Q3
C — Inside the zero check the function still divides by b, so it crashes with ZeroDivisionError. It should return a safe value such as None.
Q4
A — A try block must end with a colon. It should be 'try:' so the error handling code is valid.
Q5
B — The condition is inverted. Valid digits would be reported as invalid. It should be 'if not score.isdigit():' so only bad input is rejected.