Combines the national number with any prefix (IDD/+ and country
        code or national prefix) that was collected. A space will be inserted
        between them if the current formatting template indicates this to be
        suitable.

def _append_national_number(self, national_number):
        """Combines the national number with any prefix (IDD/+ and country
        code or national prefix) that was collected. A space will be inserted
        between them if the current formatting template indicates this to be
        suitable.
        """
        prefix_before_nn_len = len(self._prefix_before_national_number)
        if (self._should_add_space_after_national_prefix and prefix_before_nn_len > 0 and
            self._prefix_before_national_number[-1] != _SEPARATOR_BEFORE_NATIONAL_NUMBER):
            # We want to add a space after the national prefix if the national
            # prefix formatting rule indicates that this would normally be
            # done, with the exception of the case where we already appended a
            # space because the NDD was surprisingly long.
            return self._prefix_before_national_number + _SEPARATOR_BEFORE_NATIONAL_NUMBER + national_number
        else:
            return self._prefix_before_national_number + national_number