code: def update_doc(input, **params):
      
      PARAM_SOURCE = 'source'
      SOURCE_COL = 'src.col'
      SOURCE_FIELD = 'src.field'
      PARAM_RESULT = 'result'
  
      res = input[params.get(PARAM_RESULT)]
      for src in params.get(PARAM_SOURCE):
          res[src[SOURCE_FIELD]] = input[src[SOURCE_COL]][src[SOURCE_FIELD]]
      return res
docs: Updates document with value from another document
      :param input:
      :param params:
      :return: