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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 _dasd_reverse_conversion(cls, val, **kwargs):
        '''
        converts DASD String values to the reg_sz value
        '''
        if val is not None:
            if val.upper() == 'ADMINISTRATORS':
                # "" also shows 'administrators' in the GUI
                return '0'
            elif val.upper() == 'ADMINISTRATORS AND POWER USERS':
                return '1'
            elif val.upper() == 'ADMINISTRATORS AND INTERACTIVE USERS':
                return '2'
            elif val.upper() == 'NOT DEFINED':
                # a setting of anything other than nothing, 0, 1, 2 or if it
                # doesn't exist show 'not defined'
                return '9999'
            else:
                return 'Invalid Value'
        else:
            return 'Not Defined'