code: def _pwm_to_str(self, precision=4):
          
          if not self.pwm:
              return ""
          
          fmt = "{{:.{:d}f}}".format(precision)
          return "\n".join(
                  ["\t".join([fmt.format(p) for p in row])
                  for row in self.pwm]
                  )
docs: Return string representation of pwm.
  
          Parameters
          ----------
          precision : int, optional, default 4
              Floating-point precision.
  
          Returns
          -------
          pwm_string : str