docs: def transfer_metadata_to_dict(self, meta):
          """transfer str to dict.
          output should be like: {'a':1, 'b':2, 'c':3}
          """
          dic = {}
          arr = meta.strip(' ,').split(',')
          for i in arr:
              temp = i.split('=')
              key = temp[0].strip()
              value = temp[1].strip()
              dic[key] = value
          return dic