'Sets up x-axis ticks and labels that treat the x data as dates.
*tz* is a :class:`tzinfo` instance or a timezone string.
This timezone is used to create date labels.'

def axis_date(self, tz=None):

    import datetime
    if isinstance(tz, six.string_types):
        import pytz
        tz = pytz.timezone(tz)
    self.update_units(datetime.datetime(2009, 1, 1, 0, 0, 0, 0, tz))
