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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 get_readonly_fields(self, request, obj=None):
 """ This is required a subclass of VersionedAdmin has readonly_fields ours won't be undone """

        if obj:
            return list(self.readonly_fields) + ['id', 'identity',
                                                 'is_current']
        return self.readonly_fields