@abc.abstractmethod
def calendar(self, start_time=None, end_time=None, freq='day', future=False):
    'Get calendar of certain market in given time range.\n\n        Parameters\n        ----------\n        start_time : str\n            start of the time range\n        end_time : str\n            end of the time range\n        freq : str\n            time frequency, available: year/quarter/month/week/day\n        future : bool\n            whether including future trading day\n\n        Returns\n        ----------\n        list\n            calendar list\n        '
    raise NotImplementedError('Subclass of CalendarProvider must implement `calendar` method')
Get calendar of certain market in given time range.

Parameters
----------
start_time : str
    start of the time range
end_time : str
    end of the time range
freq : str
    time frequency, available: year/quarter/month/week/day
future : bool
    whether including future trading day

Returns
----------
list
    calendar list
@abc.abstractmethod
def calendar(self, start_time=None, end_time=None, freq='day', future=False):
    'Get calendar of certain market in given time range.\n\n        Parameters\n        ----------\n        start_time : str\n            start of the time range\n        end_time : str\n            end of the time range\n        freq : str\n            time frequency, available: year/quarter/month/week/day\n        future : bool\n            whether including future trading day\n\n        Returns\n        ----------\n        list\n            calendar list\n        '
    raise NotImplementedError('Subclass of CalendarProvider must implement `calendar` method')