Input validation is important to prevent incorrect or invalid values from being entered into an application which could lead to user frustration or security issues. Exceptions handle errors and unexpected conditions during program execution. Common exceptions include ImportError, ValueError, and IOError. The try-except block allows code to be executed within the try statement and exceptions raised to be handled in the except block through predefined or custom exceptions.

1. INPUT VALIDATION

2. WHY VALIDATE INPUT
 Validating user input is fundamental in
application development.
 It prevents users/systems from inadvertently
entering incorrect values or values that
should not be allowed into the application.
 Incorrect input can lead to user frustration or
serious security concerns

3. EXCEPTIONS
 An exception is a signal that a specific condition has
occurred that can’t be easily handled by normal
program flow.
 Ex. Trying to perform a calculation on a string
 Typically your application will error and crash,
however with exception handling we can catch the
error and safely exit the application, fix the issue, or
try again.
 Exceptions are preprogrammed conditional
statements for error catching, however you can
create your own error messages.

4. COMMON EXCEPTIONS
 ImportError – module not found
 ValueError – Inappropriate value
 KeyboardInterupt – When user terminates
application
 IOError – file cannot be opened

5. TRY-EXCEPT
 Code:
 try:
statement 1 to attempt
statement 2 to attempt
.
.
.
except: OPTIONAL EXCEPTION
USER CREATED EXCEPTION

6. TRY-CATCH EXAMPLE
 try:
val = int(input(“Enter a number”)
except: ValueError
 try:
val = int(input(“Enter a number”)
except: ValueError
print(“Not a valid number”)
 try:
val = int(input(“Enter a number”)
except: MyException
print(“Not a valid number”)
quit