def vline(self, y):
        self.path.append('V' + str(y))
Most session backends don't need to override this method, but we do,
dataset/ETHPy150Open CGATOxford/cgat/CGAT/SVGdraw.py/pathdata.vline--crossover with--dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/Django-1.6.10/django/contrib/sessions/backends/signed_cookies.py/SessionStore._get_session_key