1. Exception Handling
COSC 1323

2. Overview
When Python runs into an error, it stops and displays an error message
More precisely, it raises an exception
Exceptions indicate something exceptional occurred and Python cannot continue
Using exception handling, you can intercept and handle exceptions so that your program doesn’t end abruptly

3. Simple Exception Example
# try/except #
try :
num = float(input(“Enter a number: “)
except :
print(“Something went wrong”)
else :
print(“Number entered was %.2f” % num)

4. Specifying The Exception Type
# try/except
try :
num = float(input(“Enter a number: “)
except ValueError:
print(“That was not a number!”)
else :
print(“Number entered was %.2f” % num)

5. Getting an Exception’s Argument
try :
num = float(input(“\nEnter a number “))
except ValueError as e :
print(“That was not a number! Python says: “)
print(e)

6. Some Exception Types
IOError – Raised when an IO operation fails, such as when an attempt is made to open a nonexistent file in read mode
IndexError – Raised when a sequence is indexed with a number of a nonexistent element.
KeyError – Raised when a dictionary key is not found
See page 207 of our book for more examples
More Python Exceptions: