def METHOD_NAME(self):
    try:
        return self._phis
    except AttributeError:
        pass
    try:
        gammas = self._gammas
    except AttributeError:
        gammas = self.gammas()
    fugacity_coeffs_pure = self.nus()
    self._phis = [gammas[i]*fugacity_coeffs_pure[i]
            for i in range(self.N)]
    return self._phis