docs: def find(self, **kwargs):
          """
          Finds row matching specific field value
  
          Args:
              **kwargs: (**only one argument accepted**) fielname=value, e.g., formula="OH"
  
          Returns: list element or None
          """
  
          if len(kwargs) != 1:
              raise ValueError("One and only one keyword argument accepted")
  
          key = list(kwargs.keys())[0]
          value = list(kwargs.values())[0]
          ret = None
          for row in self.values():
              if row[key] == value:
                  ret = row
                  break
          return ret