Combining validation checks in a validation function

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. A validation function is checking a typed age. Which check order is correct?

A Existence, then type, then range

B Range, then type, then existence

2. What does is_valid_age(text) return when every check passes?

A True

B The age as text

3. Which line is the existence check in is_valid_age(text)?

A if int(text) > 120: return False

B if text == "": return False

4. Why should the type check come before the range check?

A Range checks run faster when they come second

B Comparing text such as "abc" with a number would cause a runtime error

5. Which approach lets you reuse validation for many inputs?

A Put the checks in one function and call it for each input

B Copy and paste the checks next to every input() call

Match the Pairs

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

Left column		Right column
1def is_valid_age(text):		ADefines a validation function that takes the user's text and will return True or False
2if text == "": return False		BThe existence check only prints a message and does not return False, so the function carries on and int("") crashes.
3Checks run in order: existence, then type, then range, so the range check never sees non-numbers		CExistence check that rejects empty input first by returning False
4One validation function can be reused for many different inputs		Dis_valid_age("17") is_valid_age("abc") is_valid_age("")
5def is_valid_age(text): if 0 <= int(text) <= 120: return True if not text.isdigit(): return False		Eif text == "": return False if not text.isdigit(): return False return 0 <= int(text) <= 120
6def is_valid_age(text): if text == "": print("Missing") return 0 <= int(text) <= 120		FThe range check runs before the type check, so int(text) crashes on input like "abc". The type check must come before the range check.

Definitions

def is_valid_age(text):

Fill in the Blanks

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

if text __ "": return False

if not text._______(): return False

age = int(text) return age >= 0 ___ age <= 120

if text == "": return _____, "Age is required"

for text in ages: if ____________(text): print("Accepted")

Spot the Error

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

Question 1

A def is_valid_age(text):

B if text != "":

C return False

D if not text.isdigit():

E return False

F return int(text) <= 120

Question 2

A def is_valid_age(text):

B if text == "":

C return False

D if text.isdigit():

E return False

F return int(text) <= 120

Question 3

A def is_valid_age(text):

B if text.strip() = "":

C return False

D if not text.isdigit():

E return False

F return int(text) <= 120

Question 4

A def check_age(text):

B if len(text) == 1:

C return "Enter an age"

D if not text.isdigit():

E return "Not a number"

F return ""

Question 5

A def is_valid_mark(text):

B if not text.isdigit():

C return True

D mark = int(text)

E return 0 <= mark <= 100

Answer Key

Combining validation checks in a validation function

Section A: Quick Questions

A — Existence, then type, then range

A — True

B — if text == "": return False

B — Comparing text such as "abc" with a number would cause a runtime error

A — Put the checks in one function and call it for each input

Section B: Match the Pairs

def is_valid_age(text): → Defines a validation function that takes the user's text and will return True or False

if text == "": return False → Existence check that rejects empty input first by returning False

Checks run in order: existence, then type, then range, so the range check never sees non-numbers → if text == "": return False if not text.isdigit(): return False return 0 <= int(text) <= 120

One validation function can be reused for many different inputs → is_valid_age("17") is_valid_age("abc") is_valid_age("")

def is_valid_age(text): if 0 <= int(text) <= 120: return True if not text.isdigit(): return False → The range check runs before the type check, so int(text) crashes on input like "abc". The type check must come before the range check.

def is_valid_age(text): if text == "": print("Missing") return 0 <= int(text) <= 120 → The existence check only prints a message and does not return False, so the function carries on and int("") crashes.

Section C: Definitions

def is_valid_age(text): — A validation function that runs the existence, type and range checks in order and returns True or False, so the same checks can be reused for many inputs and tested.

Section D: Fill in the Blanks

if text == "":
    return False

if not text.isdigit():
    return False

age = int(text)
return age >= 0 and age <= 120

if text == "":
    return False, "Age is required"

for text in ages:
    if is_valid_age(text):
        print("Accepted")

Section E: Spot the Error

B — The existence check must catch an empty entry. Using != returns False for every non-empty value. It should be if text == "": so that only blank input is rejected.

D — The type check should reject text that is NOT made of digits, so it needs not. As written, valid numbers return False. It should be if not text.isdigit():.

B — A single = assigns a value and is a syntax error inside an if. A comparison needs ==, so it should be if text.strip() == "":.

B — The existence check should only trigger when nothing was entered. Testing for length 1 flags one-digit ages and misses the empty string. It should be if text == "": (or len(text) == 0).

C — When the type check fails the input is not a number, so the function must return False. Returning True would let invalid data through. It should be return False.