@abc.abstractmethod
def list_instruments(self, instruments, start_time=None, end_time=None, freq='day', as_list=False):
    'List the instruments based on a certain stockpool config.\n\n        Parameters\n        ----------\n        instruments : dict\n            stockpool config\n        start_time : str\n            start of the time range\n        end_time : str\n            end of the time range\n        as_list : bool\n            return instruments as list or dict\n\n        Returns\n        -------\n        dict or list\n            instruments list or dictionary with time spans\n        '
    raise NotImplementedError('Subclass of InstrumentProvider must implement `list_instruments` method')
List the instruments based on a certain stockpool config.

Parameters
----------
instruments : dict
    stockpool config
start_time : str
    start of the time range
end_time : str
    end of the time range
as_list : bool
    return instruments as list or dict

Returns
-------
dict or list
    instruments list or dictionary with time spans
@abc.abstractmethod
def list_instruments(self, instruments, start_time=None, end_time=None, freq='day', as_list=False):
    'List the instruments based on a certain stockpool config.\n\n        Parameters\n        ----------\n        instruments : dict\n            stockpool config\n        start_time : str\n            start of the time range\n        end_time : str\n            end of the time range\n        as_list : bool\n            return instruments as list or dict\n\n        Returns\n        -------\n        dict or list\n            instruments list or dictionary with time spans\n        '
    raise NotImplementedError('Subclass of InstrumentProvider must implement `list_instruments` method')