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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 from_dynacRepr(cls, pynacRepr):
 """ Construct a ``CavityAnalytic`` instance from the Pynac lattice element """

        cavID = int(pynacRepr[1][0][0])
        xesln = float(pynacRepr[1][1][0])
        phase = float(pynacRepr[1][1][1])
        fieldReduction = float(pynacRepr[1][1][2])
        isec = int(pynacRepr[1][1][3])
        return cls(phase, fieldReduction, cavID, xesln, isec)