python - Error handling using integers as input

Question

Ive set up this program that checks the mark out of 100 for a test. If the user inputs less than 60 it should say fail if more than 59, pass.

mark = int(input("Please enter the exam mark out of 100 "))
if mark < 60:
    print("
Fail")
elif mark < 101:
    print("
Pass")
else:
    print("
The mark is out of range")

how do i get the program not to have errors if the user does not input the Integer.

Please help, is there a quick solution that 14 year olds would understand?

Answer 1

Save the input in a variable and convert to an integer separately:

import sys

i = input("Please enter the exam mark out of 100 ")
try:
    mark = int(i)
except ValueError:
    print('
You did not enter a valid integer')
    sys.exit(0)
if mark < 60:
    print("
Fail")
elif mark < 101:
    print("
Pass")
else:
    print("
The mark is out of range")

If it fails (i.e., you get a ValueError) then print a message and exit. You can explain (to a 14-year old) that int() needs a valid integer as input and it will raise a ValueError otherwise. That makes sense because only strings that contain an integer can be converted by int().