'Is the asset restricted (RestrictionStates.FROZEN) on the given dt?
Parameters
asset : Asset of iterable of Assets
The asset(s) for which we are querying a restriction
dt : pd.Timestamp
The timestamp of the restriction query
Returns
is_restricted : bool or pd.Series[bool] indexed by asset
Is the asset or assets restricted on this dt?'

@abc.abstractmethod
def is_restricted(self, assets, dt):

    raise NotImplementedError('is_restricted')
