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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 label_field(self, f):
 """ Select one field as the label field. Note that this field will be exclude from feature fields. :param f: Selected label field :type f: str :rtype: DataFrame """

        if f is None:
            raise ValueError("Label field name cannot be None.")
        self._assert_ml_fields_valid(f)
        return _change_singleton_roles(self, {_get_field_name(f): FieldRole.LABEL}, clear_feature=True)