code: def _merge_list(lhs, rhs):
      if not lhs:
          return rhs
      if not rhs:
          return lhs
  
      l_len = len(lhs)
      r_len = len(rhs)
      ret = [None] * (l_len + r_len)
      i, j, k = 0, 0, 0
      while i < l_len and j < r_len:
          if lhs[i][0] < rhs[j][0]:
              ret[k] = lhs[i]
              i += 1
          else:
              ret[k] = rhs[j]
              j += 1
  
          k += 1
  
      while i < l_len:
          ret[k] = lhs[i]
          i += 1
          k += 1
  
      while j < r_len:
          ret[k] = rhs[j]
          j += 1
          k += 1
  
      return ret
  
file_path: FATE/python/fate/arch/dataframe/ops/_indexer.py
imports: import functools
  import uuid
  from ..manager import Block, DataManager
  from .._dataframe import DataFrame
label_desc: Use image node_id 5 for calling a global function with example usage: _merge_list(lhs, rhs) and returns: ret, rhs, lhs