@abc.abstractmethod
def feature(self, instrument, field, start_time, end_time, freq):
    'Get feature data.\n\n        Parameters\n        ----------\n        instrument : str\n            a certain instrument\n        field : str\n            a certain field of feature\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\n        Returns\n        -------\n        pd.Series\n            data of a certain feature\n        '
    raise NotImplementedError('Subclass of FeatureProvider must implement `feature` method')
Get feature data.

Parameters
----------
instrument : str
    a certain instrument
field : str
    a certain field of feature
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

Returns
-------
pd.Series
    data of a certain feature
@abc.abstractmethod
def feature(self, instrument, field, start_time, end_time, freq):
    'Get feature data.\n\n        Parameters\n        ----------\n        instrument : str\n            a certain instrument\n        field : str\n            a certain field of feature\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\n        Returns\n        -------\n        pd.Series\n            data of a certain feature\n        '
    raise NotImplementedError('Subclass of FeatureProvider must implement `feature` method')