TimeSeriesItem(self, key: str, count: int, value: float = None) -> None
Generic container class holding a
key <> value pair, a
count of records contributing to the given value.
For example, this class could hold the total tonnage exported (value) on 2019-01-01 (key), and the count of cargo movements contributing to this tonnage aggregate, ie the number of cargo movements on this day (count).