'RiskMetrics are calculated for rolling windows in four lengths::
- 1_month
- 3_month
- 6_month
- 12_month
The return value of this function is a dictionary keyed by the above
list of durations. The value of each entry is a list of RiskMetric
dicts of the same duration as denoted by the top_level key.
See :py:meth:`RiskMetrics.to_dict` for the detailed list of fields
provided for each period.'

def to_dict(self):

    return {'one_month': [x.to_dict() for x in self.month_periods], 'three_month': [x.to_dict() for x in self.three_month_periods], 'six_month': [x.to_dict() for x in self.six_month_periods], 'twelve_month': [x.to_dict() for x in self.year_periods]}
