'Returns all valid export formats
:returns: for each export format, a pair of identifier and printable name
:rtype: [(str, str)]'

@http.route('/web/export/formats', type='json', auth='user')
def formats(self):

    return [{'tag': 'csv', 'label': 'CSV'}, {'tag': 'xls', 'label': 'Excel', 'error': (None if xlwt else 'XLWT    required')}]
