docstr: Calculate mean metric for each metric
docstr_tok: ["Calculate","mean","metric","for","each","metric"]
code: def store_mean_metric(self, col_name: str, mean_metric: float):
      """Calculate mean metric for each metric"""
  
      self.mean_evaluation_metrics[f"mean_{col_name}"].append(
          mean_metric
      )
  
imports: import ast
  from collections import defaultdict
  from typing import List
  import nltk
  import pandas
  from nltk import word_tokenize
  from nltk.translate.bleu_score import sentence_bleu
  from nltk.translate.meteor_score import meteor_score
  from rouge_score import rouge_scorer
  from scipy.spatial import distance
  from mindsdb.integrations.handlers.writer_handler.settings import WriterHandlerParameters
  from mindsdb.utilities import log
label_desc: Use image node_id 18 for calling the WriterEvaluator obj's underlying member method code with example usage: obj.store_mean_metric(col_name, mean_metric) without return types