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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 update_grade_system(self, grade_system_form):
 """Updates an existing grade system. arg: grade_system_form (osid.grading.GradeSystemForm):
 the form containing the elements to be updated raise: IllegalState - ``grade_system_form`` already used in an update transaction raise: InvalidArgument - the form contains an invalid value raise: NullArgument - ``grade_system_form`` is ``null`` raise: OperationFailed - unable to complete request raise: PermissionDenied - authorization failure raise: Unsupported - ``grade_system_form`` did not originate from ``get_grade_system_form_for_update()`` *compliance: mandatory -- This method must be implemented.* """

        # Implemented from template for
        # osid.resource.ResourceAdminSession.update_resource_template
        collection = JSONClientValidated('grading',
                                         collection='GradeSystem',
                                         runtime=self._runtime)
        if not isinstance(grade_system_form, ABCGradeSystemForm):
            raise errors.InvalidArgument('argument type is not an GradeSystemForm')
        if not grade_system_form.is_for_update():
            raise errors.InvalidArgument('the GradeSystemForm is for update only, not create')
        try:
            if self._forms[grade_system_form.get_id().get_identifier()] == UPDATED:
                raise errors.IllegalState('grade_system_form already used in an update transaction')
        except KeyError:
            raise errors.Unsupported('grade_system_form did not originate from this session')
        if not grade_system_form.is_valid():
            raise errors.InvalidArgument('one or more of the form elements is invalid')
        collection.save(grade_system_form._my_map)

        self._forms[grade_system_form.get_id().get_identifier()] = UPDATED

        # Note: this is out of spec. The OSIDs don't require an object to be returned:
        return objects.GradeSystem(
            osid_object_map=grade_system_form._my_map,
            runtime=self._runtime,
            proxy=self._proxy)