default value shops in party

party.py

@@ -4,10 +4,17 @@
 from trytond.model import fields
 from trytond.pyson import Eval
 from trytond.pool import PoolMeta
+from trytond.transaction import Transaction
 
 __all__ = ['Party']
 
 
 class Party(metaclass=PoolMeta):
     __name__ = "party.party"
+
     shops = fields.Many2Many('purchase.shop_party', 'party', 'shop', 'Shops')
+
+    @staticmethod
+    def default_shops():
+        return Transaction().context.get('shops')
+