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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def interpolate(self):
 """ Interpolate across any missing zones. TODO Allow spline interpolation. """

        nans, x = utils.nan_idx(self)
        self[nans] = np.interp(x(nans), x(~nans), self[~nans])
        return self