fields change product in purchase

purchase.py

@@ -3,6 +3,7 @@
 from trytond.pool import Pool, PoolMeta
 from trytond.model import (
     ModelView, ModelSQL, Workflow, fields)
+from trytond.modules.product import price_digits, round_price
 from trytond.pyson import Eval, If, Bool
 from trytond.exceptions import UserError
 from trytond.i18n import gettext
@@ -60,7 +61,7 @@ class Purchase(metaclass=PoolMeta):
                             refurbish=line.refurbish,
                             serial=None if line.quantity > 1 else line.serial_equipment,
                             health_register=line.health_register,
-                            software_version=line.software_version,
+                            software_version=line.product.software_version,
                             maintenance_frequency="none")
                         equipment.save()
                 else:
@@ -96,6 +97,24 @@ class Line(metaclass=PoolMeta):
             company = Company(company)
             return company.party.addresses[0].id
 
+    @fields.depends(
+        'product', 'quantity', methods=['_get_context_purchase_price'])
+    def on_change_quantity(self):
+        Product = Pool().get('product.product')
+        if self.quantity > 1 or self.quantity < 1:
+            self.serial_equipment = None
+            
+        if not self.product:
+            self.serial_equipment = None
+            return
+
+        with Transaction().set_context(self._get_context_purchase_price()):
+            self.unit_price = Product.get_purchase_price([self.product],
+                abs(self.quantity or 0))[self.product.id]
+
+            if self.unit_price:
+                self.unit_price = round_price(self.unit_price)
+                
     def on_change_product(self):
         if not self.product:
             self.product_equipment = False