I am learning Python and when I learned that we can build Custom classes for exception, I got into a confusion of Why ?

for example1 :

class MyException(Exception):       def __init__(self, error):            self.error = error       def __str__(self):           # DO THE WORK TO BE DONE FOR THE EXCEPTION           print  "Here is my custom made exception" + self.error 

example 2 :

try:   # SOMETHING except:   # DO THE WORK TO BE DONE FOR THE EXCEPTION   raise Exception("Here is my custom made exception - Whats the reason ?") 

If example 2 does the same work as example1, Why do we need custom exception. Is there a scenario why I needed a custom exception when I could just do everything I needed inside except block.