def onchange_picking_type_id(self, cr, uid,ids, picking_type_id, context=None):

            if picking_type_id in (12,13,18,17):

                domain={}

                domain['product_id']=[('product_id','in',[])]

                sql="select t0.id from product_product t0 LEFT JOIN product_template  t1 on t0.product_tmpl_id=t1.id where t1.categ_id=4"

                cr.execute(sql)

                dict=cr.dictfetchall()

                valu=[]

                for i in range(len(dict)):

                    dict2=dict[i]

                    valu.append(dict2['id'])

                domain['product_id']=[('id','in',valu)]

            else:

                 domain={}

            return {'domain':domain}

<field name="picking_type_id" invisible="1" on_change="onchange_picking_type_id(picking_type_id)"/>

aa='1.2.6'

bb='1.3.5.6'

cc='1.3.6.9.5'

dd='5.6'

list1=[aa.split('.'),bb.split('.'),cc.split('.'),dd.split('.')]

sorted(list1)

[['', '', ''], ['', '', '', ''], ['', '', '', '', ''], ['', '']]

list1=[['', '', ''], ['',''],['', '', '', ''], ['', '', '', '', ''], ['', '']]

for index,item in enumerate(sorted(list1)):

    print index,item