docs: def _db_filename_from_dataframe(base_filename, df):
      """
      Generate database filename for a sqlite3 database we're going to
      fill with the contents of a DataFrame, using the DataFrame's
      column names and types.
      """
      db_filename = base_filename + ("_nrows%d" % len(df))
      for column_name in df.columns:
          column_db_type = db_type(df[column_name].dtype)
          column_name = column_name.replace(" ", "_")
          db_filename += ".%s_%s" % (column_name, column_db_type)
      return db_filename + ".db"