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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 monthly_clear_sky_conditions(self):
 """A list of 12 monthly clear sky conditions that are used on the design days."""

        if self._monthly_tau_diffuse is [] or self._monthly_tau_beam is []:
            return [OriginalClearSkyCondition(i, 21) for i in xrange(1, 13)]
        return [RevisedClearSkyCondition(i, 21, x, y) for i, x, y in zip(
            list(xrange(1, 13)), self._monthly_tau_beam, self._monthly_tau_diffuse)]