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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 read_structure(self, cls=Structure):
 """Returns the crystalline structure."""

        if self.ngroups != 1:
            raise NotImplementedError("In file %s: ngroups != 1" % self.path)

        return structure_from_ncdata(self, cls=cls)