code: def merge_asof(left, right, on=None,
                 left_on=None, right_on=None,
                 left_index=False, right_index=False,
                 by=None, left_by=None, right_by=None,
                 suffixes=('_x', '_y'),
                 tolerance=None,
                 allow_exact_matches=True,
                 direction='backward'):
      op = _AsOfMerge(left, right,
                      on=on, left_on=left_on, right_on=right_on,
                      left_index=left_index, right_index=right_index,
                      by=by, left_by=left_by, right_by=right_by,
                      suffixes=suffixes,
                      how='asof', tolerance=tolerance,
                      allow_exact_matches=allow_exact_matches,
                      direction=direction)
      return op.get_result()