docs: def y_grid(self, grid=None):
          """The vertical lines that run accross the chart from the y-ticks.
  
          If a boolean value is given, these gridlines will be turned on or off.
          Otherwise, the method will return their current state.
  
          :param bool grid: Turns the gridlines on or off.
          :rtype: ``bool``"""
  
          if grid is None:
              return self._y_grid
          else:
              if not isinstance(grid, bool):
                  raise TypeError("grid must be boolean, not '%s'" % grid)
              self._y_grid = grid