code: def frame(self, min_x=None, min_y=None, max_x=None, max_y=None):
          
          ret = self.line_ending.join(self.rows(min_x, min_y, max_x, max_y))
  
          if IS_PY3:
              return ret
  
          return ret.encode('utf-8')
docs: String representation of the current :class:`Canvas` object pixels.
  
          :param min_x: (optional) minimum x coordinate of the canvas
          :param min_y: (optional) minimum y coordinate of the canvas
          :param max_x: (optional) maximum x coordinate of the canvas
          :param max_y: (optional) maximum y coordinate of the canvas