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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 xunit(self):
 """Unit of x-axis index :type: `~astropy.units.Unit` """

        try:
            return self._dx.unit
        except AttributeError:
            try:
                return self._x0.unit
            except AttributeError:
                return self._default_xunit