docs: def cols_to_cat(df, col_list,dest = False):
      """ Coerces a list of columns to categorical
      Parameters:
      df - DataFrame
          DataFrame to operate on
      col_list - list of strings
          names of columns to coerce
      dest - bool, default False
          Whether to apply the result to the DataFrame or return it.
          True is apply, False is return.
      """
      # Convert a list of columns to categorical
      if not dest:
          return _pd.DataFrame({col_name:col_to_cat(df,col_name) for col_name in col_list})
      for col_name in col_list:
          col_to_cat(df,col_name,dest)