How to pass a variable to an exception when raised and retrieve it when excepted?

Question

Right now I just have a blank exception class. I was wondering how I can give it a variable when it gets raised and then retrieve that variable when I handle it in the try...exc

Answer 1

Give its constructor an argument, store that as an attribute, then retrieve it in the except clause:

class FooException(Exception):
    def __init__(self, foo):
        self.foo = foo

try:
    raise FooException("Foo!")
except FooException as e:
    print e.foo