When an exception "as" variable occurs, it deletes local variables with the same name. This is certainly surprising, and doesn't appear to be a documented behavior (but maybe I don't know where to look). The word "bug" comes to mind.  The following few lines of code illustrate it nicely:

def testme():
    err = Exception("nothing worked")
    try:
        raise ValueError("no value")
    except ValueError as err:
        pass
    print(err)

testme()