code: def get_dpi(raise_error=True):
      
      # If we are running without an X server (e.g. OSMesa), use a fixed DPI
      if 'DISPLAY' not in os.environ:
          return 96.
  
      from_xdpyinfo = _get_dpi_from(
          'xdpyinfo', r'(\d+)x(\d+) dots per inch',
          lambda x_dpi, y_dpi: (x_dpi + y_dpi) / 2)
      if from_xdpyinfo is not None:
          return from_xdpyinfo
  
      from_xrandr = _get_dpi_from(
          'xrandr', r'(\d+)x(\d+).*?(\d+)mm x (\d+)mm',
          lambda x_px, y_px, x_mm, y_mm: 25.4 * (x_px / x_mm + y_px / y_mm) / 2)
      if from_xrandr is not None:
          return from_xrandr
      if raise_error:
          raise RuntimeError('could not determine DPI')
      else:
          logger.warning('could not determine DPI')
      return 96
docs: Get screen DPI from the OS
  
      Parameters
      ----------
      raise_error : bool
          If True, raise an error if DPI could not be determined.
  
      Returns
      -------
      dpi : float
          Dots per inch of the primary screen.