Use PySON

sale.py

@@ -2,6 +2,8 @@
 #this repository contains the full copyright notices and license terms.
 "Sale"
 from trytond.model import ModelView, ModelSQL, fields
+from trytond.pyson import Not, Equal, Eval
+
 
 class SaleLine(ModelSQL, ModelView):
     _name = 'sale.line'
@@ -9,7 +11,7 @@ class SaleLine(ModelSQL, ModelView):
     analytic_accounts = fields.Many2One('analytic_account.account.selection',
             'Analytic Accounts',
             states={
-                'invisible': "type != 'line'",
+                'invisible': Not(Equal(Eval('type'), 'line')),
             })
 
     def _view_look_dom_arch(self, cursor, user, tree, type, context=None):