code: def on_exception(func):
      
      class OnExceptionDecorator(LambdaDecorator):
          def on_exception(self, exception):
              return func(exception)
  
      return OnExceptionDecorator
docs: Run a function when a handler thows an exception. It's return value is
      returned to AWS.
  
      Usage::
  
          >>> # to create a reusable decorator
          >>> @on_exception
          ... def handle_errors(exception):
          ...     print(exception)
          ...     return {'statusCode': 500, 'body': 'uh oh'}
          >>> @handle_errors
          ... def handler(event, context):
          ...     raise Exception('it broke!')
          >>> handler({}, object())
          it broke!
          {'statusCode': 500, 'body': 'uh oh'}
          >>> # or a one off
          >>> @on_exception(lambda e: {'statusCode': 500})
          ... def handler(body, context):
          ...     raise Exception
          >>> handler({}, object())
          {'statusCode': 500}