Existence checking in code

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which condition correctly checks that a user typed nothing into a field?

A if value.strip() = '':

B if value.strip() == '':

2. A user types three spaces and presses Enter. Which check catches this as missing data?

A if value.strip() == '':

B if value == '':

3. True or false: an existence check tests whether the value is sensible, such as an age between 0 and 120.

A False - it only tests that something was entered

B True - it tests that the value is sensible

4. Which code shows a message when the name field is missing?

A if name.strip() != '': print('Please enter a name')

B if name.strip() == '': print('Please enter a name')

5. How can you check that a list has at least one item before using it?

A if len(scores) == 0:

B if scores.strip() == '':

Match the Pairs

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

Left column		Right column
1if value.strip() == '':		Aif name.strip() == '': print('Name is required')
2if len(items) == 0:		BA single = is assignment and causes a syntax error. A comparison needs ==, as in value.strip() == ''.
3Show an error message when a required field is left blank		CExistence check: True when the input is empty or only spaces, so nothing real was entered
4Stop space-only input from passing an existence check by removing the spaces first		DWithout strip(), a space-only input is not equal to '', so the existence check wrongly passes. Use value.strip() == ''.
5if value == '': print('Missing') # user types three spaces		Etext = input('Enter: ').strip()
6if value.strip() = '':		FExistence check on a list: True when the list holds no items, so there is no data to use

Definitions

if value.strip() == '':

Fill in the Blanks

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

value = input("Enter your name: ") if value._____() == '': print("Please enter a value")

name = input("Name: ") if name.strip() __ '': print("Name is required")

scores = [] if ___(scores) == 0: print("No scores entered")

city = input("City: ") if city.strip() == '': _____("City is missing")

import os if not os.path.______("data.csv"): print("File not found")

Spot the Error

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

Question 1

A name = input('Name: ')

B if name.strip() == '':

C print('Welcome', name)

D else:

E print('Hello', name)

Question 2

A email = input('Email: ')

B if email.strip() == '':

C print('Email is required')

D else

E print('Saved')

Question 3

A age = input('Age: ')

B while age.strip() == '':

C print('Age is required')

D age = age.strip()

E print('Thanks')

Question 4

A city = input('City: ')

B if city.strip() = '':

C print('City is required')

D else:

E print(city)

Question 5

A code = print('Code: ')

B if code.strip() == '':

C print('Code missing')

Answer Key

Existence checking in code

Section A: Quick Questions

B — if value.strip() == '':

A — if value.strip() == '':

A — False - it only tests that something was entered

B — if name.strip() == '': print('Please enter a name')

A — if len(scores) == 0:

Section B: Match the Pairs

if value.strip() == '': → Existence check: True when the input is empty or only spaces, so nothing real was entered

if len(items) == 0: → Existence check on a list: True when the list holds no items, so there is no data to use

Show an error message when a required field is left blank → if name.strip() == '': print('Name is required')

Stop space-only input from passing an existence check by removing the spaces first → text = input('Enter: ').strip()

if value == '': print('Missing') # user types three spaces → Without strip(), a space-only input is not equal to '', so the existence check wrongly passes. Use value.strip() == ''.

if value.strip() = '': → A single = is assignment and causes a syntax error. A comparison needs ==, as in value.strip() == ''.

Section C: Definitions

if value.strip() == '': — An existence check tests that a value was actually entered. strip() removes spaces, so this is True for empty or space-only input, and an error message can be shown.

Section D: Fill in the Blanks

value = input("Enter your name: ")
if value.strip() == '':
    print("Please enter a value")

name = input("Name: ")
if name.strip() == '':
    print("Name is required")

scores = []
if len(scores) == 0:
    print("No scores entered")

city = input("City: ")
if city.strip() == '':
    print("City is missing")

import os
if not os.path.exists("data.csv"):
    print("File not found")

Section E: Spot the Error

C — This branch runs when the name is empty, so it should show a missing-data message such as print('Name is required'), not a welcome that uses the empty value.

D — The else keyword must be followed by a colon. It should be else:.

D — The loop never asks again, so age stays empty and the loop runs forever. The line should ask again with age = input('Age: ').

B — A single = is assignment, not comparison. The existence check needs == to compare with the empty string.

A — print() only displays text and does not read what the user types. The value must be read with input('Code: ').