Type checking in code
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. A student types 42 into input(). What data type is the value that input() returns?
2. Which line correctly checks that the string age contains only whole-number digits?
3. What does "3.5".isdigit() return?
4. Which error does int("abc") raise, which a type check should catch?
5. Which approach lets you check that input is a valid decimal number such as 3.5?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1age.isdigit() | Ainput() always returns text (str), so isinstance(age, int) is never True. Use age.isdigit() on the text, or try int(age), instead. | |
| 2isinstance(price, float) | Btry: h = float(text) except ValueError: h = None | |
| 3Test whether text is a whole number by trying to convert it and catching the failure | Ctry: n = int(text) except ValueError: print("Not a whole number") | |
| 4Check that input is a decimal number by trying float() on the text | Disdigit() is False for decimals and negatives because '.' and '-' are not digits. Use try/except around float(temp) to check for a decimal number. | |
| 5age = input("Age: ") if isinstance(age, int): print("Valid") | EReturns True if the value stored in price is already a float | |
| 6temp = "-4.5" if temp.isdigit(): print("Valid number") | FReturns True if the text contains only digits, so it is a safe whole number to convert with int() |
C
Definitions
type check
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
age = input("Age: ")
if age._______():
age = int(age)
2.
try:
n = ___(text)
except ValueError:
3.
try:
price = float(text)
except __________:
4.
value = 3.5
print(isinstance(value, _____))
5.
num = input("Number: ")
print(____(num))
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
age = input("Age: ")
B
if age.isdigit:
C
print(int(age) + 1)
Question 2
A
num = input("Number: ")
B
if isinstance(num, int):
C
num = int(num)
D
print(num * 2)
Question 3
A
try:
B
n = int(input("Num: "))
C
except TypeError:
D
print("Not a whole number")
Question 4
A
val = float(input("Price: "))
B
try:
C
price = float(val)
D
except ValueError:
E
print("Not a number")
Question 5
A
qty = input("Quantity: ")
B
if qty.isdigit():
C
total = qty * 5
D
else:
E
print("Whole numbers only")
Answer Key
Type checking in code
Section A: Quick Questions
Q1
B — A string (text)
Q2
A — age.isdigit()
Q3
A — False, because the . is not a digit
Q4
B — except ValueError:
Q5
A — try: float(text) with except ValueError
Section B: Match the Pairs
Q1
age.isdigit() → Returns True if the text contains only digits, so it is a safe whole number to convert with int()
Q2
isinstance(price, float) → Returns True if the value stored in price is already a float
Q3
Test whether text is a whole number by trying to convert it and catching the failure → try:
n = int(text)
except ValueError:
print("Not a whole number")
Q4
Check that input is a decimal number by trying float() on the text → try:
h = float(text)
except ValueError:
h = None
Q5
age = input("Age: ")
if isinstance(age, int):
print("Valid") → input() always returns text (str), so isinstance(age, int) is never True. Use age.isdigit() on the text, or try int(age), instead.
Q6
temp = "-4.5"
if temp.isdigit():
print("Valid number") → isdigit() is False for decimals and negatives because '.' and '-' are not digits. Use try/except around float(temp) to check for a decimal number.
Section C: Definitions
Q1
type check — A check that input is the expected data type, using .isdigit(), try/except around int() or float(), or isinstance(). input() is always text, so check before converting.Section D: Fill in the Blanks
Q1
age = input("Age: ")
if age.isdigit():
age = int(age)Q2
try:
n = int(text)
except ValueError:Q3
try:
price = float(text)
except ValueError:Q4
value = 3.5
print(isinstance(value, float))Q5
num = input("Number: ")
print(type(num))Section E: Spot the Error
Q1
B — isdigit is a method, so it needs brackets to be called. Without them the condition is just the method object, which is always True, so nothing is checked. It should be if age.isdigit():
Q2
B — input() always returns a string, so isinstance(num, int) is always False. To check that the text is a whole number, use num.isdigit().
Q3
C — int("abc") raises a ValueError, not a TypeError, so this except would not catch bad input and the program would crash. It should be except ValueError:
Q4
A — The float() conversion happens before the try block, so bad input crashes the program before it can be caught. Keep input() as text on line 1 and convert inside the try: val = input("Price: ")
Q5
C — qty is still text after the isdigit() check. Multiplying a string by 5 repeats it ("3" becomes "33333") instead of doing maths. Convert it first: total = int(qty) * 5