In below example I have written Python script to configure barcode. It will print one barcode on each page based on quantity available of selected products. Like below python code in .py file :

  import logging

from openerp.osv import fields, orm

_logger = logging.getLogger(__name__)
try:
    from reportlab.graphics.barcode import getCodes
except ImportError:
    _logger.warning('unable to import reportlab')


def _get_code(self, cr, uid, context=None):
    """get availble code """
    return [(r, r) for r in getCodes()]


class tr_barcode_config(orm.Model):
    _name = 'tr.barcode.config'
    _columns = {
        'res_model': fields.many2one('ir.model', 'Object',
                                     domain=[('barcode_model', '=', True)],
                                     required=True),
        'field': fields.many2one('ir.model.fields', 'Field',
                                 domain=[('ttype', '=', 'char')],
                                 required=True),
        'width': fields.integer("Width",
                     help="Leave Blank or 0(ZERO) for default size"),
        'height': fields.integer("Height",
                     help="Leave Blank or 0(ZERO) for default size"),
        'hr_form': fields.boolean("Human Readable",
                     help="To generate Barcode In Human readable form"),
        'barcode_type': fields.selection(_get_code, 'Type', required=True),
        }
    _sql_constraints = [
        ('res_model_uniq',
         'unique(res_model)',
         'You can have only one config by model !'),
        ]