I have this python code which seem very straight forward but when I try to load it I get an error as above. you can view the full error message below too. Please what am I doing wrong? Thanks you.

class label_maker(osv.osv):
_name = 'label.maker'
_columns = {
    'name': fields.char('Label Name',size=200,required=True, help='This is the name of the label'),
    'label_owner': fields.char('Company Name',size=200,select=True, help='selects the product on the order line'),
   #        'sequence': fields.integer('Sequence',size=128, required=True),
}
   label_maker()

   class product_product_inherit(osv.osv):
_name = 'product.product.inherit'
_inherit = 'product.product'
_columns = {
    'labelnid': fields.many2one('label.maker','Label',select=True, help='label name'),
}
   product_product_inherit()

   class order_line(osv.osv):
_name = 'order.line'
_inherit = 'sale.order.line'
_columns = {
    'order_line_label': fields.many2one('label.maker','Label',select=True, help='select the right label for the product and partner'),
     #      'order_line_label': fields.related('product_id','labelnid',type='many2one',string='Label' relation= 'label_maker',select=True, help='select the right label for the product and partner'),
}
   order_line()

   class order_line_picking_list(osv.osv):
_name = 'order.line.picking.list'
_inherit = 'stock.move'
_columns = {
    'picking_labels': fields.many2one('label.maker','Label',select=True, help='label for the product on the picking list'),
   #        'labels': fields.related('order_id','order_line_label',type='many2one', relation='label_maker', string='Label', select=True, help='label for the product on the picking list'),
}
   order_line_picking_list()

Client Traceback (most recent call last): File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\common\http.py", line 180, in dispatch File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\controllers\main.py", line 1052, in call_button File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\controllers\main.py", line 996, in call_common File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\controllers\main.py", line 1010, in _call_kw File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\common\openerplib\main.py", line 250, in proxy File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\common\openerplib\main.py", line 117, in proxy File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\common\http.py", line 608, in send

Server Traceback (most recent call last): File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\web\common\http.py", line 593, in send File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\netsvc.py", line 360, in dispatch_rpc File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\service\web_services.py", line 572, in dispatch File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\osv\osv.py", line 167, in execute_kw File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\osv\osv.py", line 121, in wrapper File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\osv\osv.py", line 176, in execute File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\osv\osv.py", line 164, in execute_cr File "C:\Program Files (x86)\OpenERP 6.1-1\server\openerp\addons\base\module\wizard\base_module_upgrade.py", line 101, in upgrade_module File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\pooler.py", line 39, in restart_pool File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\modules\registry.py", line 160, in new File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\modules\loading.py", line 338, in load_modules File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\modules\loading.py", line 253, in load_marked_modules File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\modules\loading.py", line 167, in load_module_graph File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\modules\registry.py", line 97, in load File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\osv\orm.py", line 919, in create_instance File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\osv\orm.py", line 1048, in __init__ File "C:\Program Files (x86)\OpenERP 6.1-1\server.\openerp\osv\orm.py", line 3255, in _inherits_check AttributeError: 'str' object has no attribute 'items'