def _ensure_sequence(self, mutable=False):
        """This method can be called by methods that need a sequence.  If
        `mutable` is true, it will also ensure that the response sequence
        is a standard Python list.

        .. versionadded:: 0.6
        """
        if self.is_sequence:
            # if we need a mutable object, we ensure it's a list.
            if mutable and not isinstance(self.response, list):
                self.response = list(self.response)
            return
        if self.direct_passthrough:
            raise RuntimeError('Attempted implicit sequence conversion '
                               'but the response object is in direct '
                               'passthrough mode.')
        if not self.implicit_sequence_conversion:
            raise RuntimeError('The response object required the iterable '
                               'to be a sequence, but the implicit '
                               'conversion was disabled.  Call '
                               'make_sequence() yourself.')
        self.make_sequence()