[Tutor] Impossible Else as Exception

[Jordan]

I want to know what exception should be raised if there is a bug in my 
code that allows an else statement to be triggered, because the else 
condition in my code should be impossible, unless there is an error in 
my code.  What exception should I raise so that if my code is wrong it 
will raise an exception which will give me a trace back?  Which would be 
most Pythonic?

Example:

if condition is 1:
     do something with 1
elif condition is 2:
     do something with 2
else: # Impossible unless the code above is flawed.
     Raise Exception