code: def extract(input, **params):
      
      EXTRACT_FIELD = 'field'
  
      extract_params = params
      extract_params.update({AccessParams.KEY_TYPE: AccessParams.TYPE_SINGLE})
      return __extract(input, params)[params.get(EXTRACT_FIELD)]
docs: Extract field value from document
      :param input:
      :param params:
      :return: