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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 clean(self):
        ''' Either staffCategory or staffMember must be filled in, but not both. '''
        if not self.staffCategory and not self.staffMember:
            raise ValidationError(_('Either staff category or staff member must be specified.'))
        if self.staffCategory and self.staffMember:
           raise ValidationError(_('Specify either a staff category or a staff member, not both.'))