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("\nFail")
elif mark < 101:
    print("\nPass")
else:
    print("\nThe 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?

If you're using python 2, use raw_input instead of input. Then follow one of the answers below. — kojiro
– kojiro, Commented Jul 11, 2012 at 12:46
If the user inputs less than 60 it should say fail if more than 59, pass. So what is the passing score? 59.5? :) — Burhan Khalid
– Burhan Khalid, Commented Jul 11, 2012 at 12:47

Simeon Visser · Accepted Answer · 2012-07-11 12:46:10Z

6

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('\nYou did not enter a valid integer')
    sys.exit(0)
if mark < 60:
    print("\nFail")
elif mark < 101:
    print("\nPass")
else:
    print("\nThe 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().

answered Jul 11, 2012 at 12:46

Simeon Visser

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Comments

Rob Wagner · Accepted Answer · 2012-07-11 14:50:44Z

4

try:
   mark = int(input("Please enter the exam mark out of 100 "))
except ValueError:
   print("\nPlease only use integers")

edited Jul 11, 2012 at 14:50

answered Jul 11, 2012 at 12:44

Rob Wagner

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1 Comment

mgilson Over a year ago

"Check its type" -- It will always be a string, (which is why int is needed).

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