code: def df_type(df: DataFrameType) -> Union[str, None]:
      """
      Returns the type of the dataframe.
  
      Args:
          df (DataFrameType): Pandas or Polars dataframe
  
      Returns:
          str: Type of the dataframe
      """
      if polars_imported and isinstance(df, pl.DataFrame):
          return "polars"
      elif isinstance(df, pd.DataFrame):
          return "pandas"
      else:
          return None
  
label_desc: Use image node_id 1 for calling a global function with example usage: df_type(df) and returns: str, str, None