code: def save_csv(self, filename, write_header_separately=True):
          
          txt = ''
          #print("SAVING arr = ", self.arr)
          
          with open(filename, "w") as f:
              if write_header_separately:
                  f.write(','.join([c for c in self.header]) + '\n')
              for row in self.arr:
                  #print('save_csv: saving row = ', row)
                  txt = ','.join([self.force_to_string(col) for col in row])
                  #print(txt)
                  f.write(txt + '\n')
              f.write('\n')
docs: save the default array as a CSV file