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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 coordinates(self):
 """ Get or set the internal coordinate system. Available coordinate systems are: - ``'jacobi'`` (default) - ``'democraticheliocentric'`` - ``'whds'`` """

        i = self._coordinates
        for name, _i in COORDINATES.items():
            if i==_i:
                return name
        return i