def trap(self, *errorTypes):
        """
        Trap this failure if its type is in a predetermined list.

        This allows you to trap a Failure in an error callback.  It will be
        automatically re-raised if it is not a type that you expect.

        The reason for having this particular API is because it's very useful
        in Deferred errback chains::

            def _ebFoo(self, failure):
                r = failure.trap(Spam, Eggs)
                print('The Failure is due to either Spam or Eggs!')
                if r == Spam:
                    print('Spam did it!')
                elif r == Eggs:
                    print('Eggs did it!')

        If the failure is not a Spam or an Eggs, then the Failure will be
        'passed on' to the next errback. In Python 2 the Failure will be
        raised; in Python 3 the underlying exception will be re-raised.

        @type errorTypes: L{Exception}
        """
        error = self.check(*errorTypes)
        if not error:
            if _PY3:
                self.raiseException()
            else:
                raise self
        return error

        Trap this failure if its type is in a predetermined list.

        This allows you to trap a Failure in an error callback.  It will be
        automatically re-raised if it is not a type that you expect.

        The reason for having this particular API is because it's very useful
        in Deferred errback chains::

            def _ebFoo(self, failure):
                r = failure.trap(Spam, Eggs)
                print('The Failure is due to either Spam or Eggs!')
                if r == Spam:
                    print('Spam did it!')
                elif r == Eggs:
                    print('Eggs did it!')

        If the failure is not a Spam or an Eggs, then the Failure will be
        'passed on' to the next errback. In Python 2 the Failure will be
        raised; in Python 3 the underlying exception will be re-raised.

        @type errorTypes: L{Exception}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/failure.py