def _get_fill_indexer(self, target, method, limit=None, tolerance=None):
        if self.is_monotonic_increasing and target.is_monotonic_increasing:
            method = (self._engine.get_pad_indexer if method == 'pad' else
                      self._engine.get_backfill_indexer)
            indexer = method(target._values, limit)
        else:
            indexer = self._get_fill_indexer_searchsorted(target, method,
                                                          limit)
        if tolerance is not None:
            indexer = self._filter_indexer_tolerance(target._values, indexer,
                                                     tolerance)
        return indexer
dataset/ETHPy150Open pydata/pandas/pandas/indexes/base.py/Index._get_fill_indexer/original