try/except. Write a function called oops that explicitly raises an IndexError exception when called. Then write another function that calls oops inside a try/except statement to catch the error. What happens if you change oops to raise KeyError instead of IndexError? Where do the names KeyError and IndexError come from? (Hint: recall that all unqualified names come from one of four scopes, by the LEGB rule.)

Exception objects and lists. Change the oops function you just wrote to raise an exception you define yourself, called MyError, and pass an extra data item along with the exception. You may identify your exception with either a string or a class. Then, extend the try statement in the catcher function to catch this exception and its data in addition to IndexError, and print the extra data item. Finally, if you used a string for your exception, go back and change it to a class instance; what now comes back as the extra data to the handler?

Error handling. Write a function called safe(func,*args) that runs any function using apply, catches any exception raised while the function runs, and prints the exception using the exc_type and exc_value attributes in the sys module. Then, use your safe function to run the oops function you wrote in exercises 1 and/or 2. Put safe in a module file called tools.py, and pass it the oops function interactively. What sort of error messages do you get? Finally, expand safe to also print a Python stack trace when an error occurs by calling the built-in print_exc( ) function in the standard traceback module (see the Python library reference manual for details).