User defined exception if the user enters a string in input instead of a number Here I am using class for a user-defined exception, I know that if I use ==> except Exception: it will work but i want to use user-defined exception ==> except error

class error(Exception):
   pass

class b(error):
   try:
       age = int(input("Enter your age:\n>>"))
       if(age >= 18):
          print("You are Eligible for Voting")
       elif(age < 18):
          print("You are not Eligible for Voting")
       else:
          raise error
   except error:                   # except Exception: --> it works
       print("Invalid input")
       print("Enter a number as your age")

obj = b()

output:-

Enter your age:
>> sdsd

Traceback (most recent call last):
  File "c:\Users\HP\OneDrive\Desktop\All Desktop <br>apps\Python\Python_Programs\exception_handling.py", line 6, in <module>
    class b(error):
  File "c:\Users\HP\OneDrive\Desktop\All Desktop apps\Python\Python_Programs\exception_handling.py", line 8, in b
    age = int(input("Enter your age:\n>>"))
ValueError: invalid literal for int() with base 10: 'sdsd'

CodePudding user response：

When you input 'sdsd', you will get a ValueError from function int():

age = int(input("Enter your age:\n>>"))

so when you try to catch Error(that you defined), it doesn't work.

ValueError: invalid literal for int() with base 10: 'sdsd'

ValueError is a sub class of Exception, and when you catch Exception, your code can catch this ValueError, so it works.

CodePudding user response：

The except clause only catches an exception if the exception is an instance of the exception class given to the except clause, or a subclass of it.

In your case, the int constructor raises ValueError when given a non-integer-formatted string as input, and since ValueError is a subclass of the Exception class, you can catch it with except Exception. But you cannot catch it with except error because the ValueError is not a subclass of your user-defined error class.