def y_grid(self, grid=None):
if grid is None:<EOL><INDENT>return self._y_grid<EOL><DEDENT>else:<EOL><INDENT>if not isinstance(grid, bool):<EOL><INDENT>raise TypeError("<STR_LIT>" % grid)<EOL><DEDENT>self._y_grid = grid<EOL><DEDENT>
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``