How to use the rdtools.normalization.interpolate function in rdtools

interpolation_frequency = init.get('interpolation_frequency', None)
        if interpolation_frequency is not None:
            max_timedelta = init['max_timedelta']
            interpolation_keys = [
                'pv', 'poa', 'ghi', 'dni', 'dhi', 'ambient_temperature',
                'windspeed'
            ]
            for key in ['pv_tilt', 'pv_azimuth']:
                if isinstance(init[key], (pd.Series, pd.DataFrame)):
                    interpolation_keys.append(key)
            for key in interpolation_keys:
                if key not in init:
                    continue
                values = init[key]
                interpolated = normalization.interpolate(
                    values, interpolation_frequency, max_timedelta
                )
                init[key] = interpolated

        common_graph = {
            'pvlib_location': (
                    pvlib.location.Location, 'latitude', 'longitude'
            ),
            'times': (
                lambda series: series.index, 'pv'
            ),
            'pv_energy': (
                power_to_energy, 'pv', 'max_timedelta'
            ),
            'solar_position': (
                lambda loc, times: loc.get_solarposition(times),