Use PySON

stock.py

@@ -1,12 +1,15 @@
 #This file is part of Tryton.  The COPYRIGHT file at the top level
 #of this repository contains the full copyright notices and license terms.
 from trytond.model import ModelView, ModelSQL, fields
+from trytond.pyson import Not, Eval, Bool
 
 
 class Location(ModelSQL, ModelView):
     "Stock Location"
     _name = 'stock.location'
-    sequence = fields.Integer('Sequence', states= {'readonly': "not active"})
+    sequence = fields.Integer('Sequence', states={
+        'readonly': Not(Bool(Eval('active'))),
+        })
 
     def __init__(self):
         super(Location, self).__init__()