diff --git a/__init__.py b/__init__.py
index 3d7008a..f4b7c48 100644
--- a/__init__.py
+++ b/__init__.py
@@ -1,19 +1,19 @@
 # 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.pool import Pool
-from .sale import (Sale, SaleProfitJournalStart, SaleProfitJournal,
-    SaleProfitJournalReport)
-from .product import Template
+from . import sale
+from . import product
+
 
 def register():
     Pool.register(
-        Sale,
-        Template,
-        SaleProfitJournalStart,
+        sale.Sale,
+        product.Template,
+        sale.SaleProfitJournalStart,
         module='sale_cost', type_='model')
     Pool.register(
-        SaleProfitJournalReport,
+        sale.SaleProfitJournalReport,
         module='sale_cost', type_='report')
     Pool.register(
-        SaleProfitJournal,
+        sale.SaleProfitJournal,
         module='sale_cost', type_='wizard')
diff --git a/product.py b/product.py
index ef5ab01..079fcbc 100644
--- a/product.py
+++ b/product.py
@@ -3,9 +3,6 @@
 from trytond.model import fields
 from trytond.pool import PoolMeta
 
-__all__ = ['Template']
 
-
-class Template:
-    __metaclass__ = PoolMeta
+class Template(metaclass=PoolMeta):
     __name__ = 'product.template'
diff --git a/sale.py b/sale.py
index 3e2c6d3..64f58df 100644
--- a/sale.py
+++ b/sale.py
@@ -9,9 +9,6 @@ from trytond.report import Report
 from trytond.wizard import Wizard, StateView, Button, StateReport
 from trytond.transaction import Transaction
 
-__all__ = ['Sale', 'SaleProfitJournalStart', 'SaleProfitJournal',
-    'SaleProfitJournalReport']
-
 STATES = {
         'readonly': Eval('state').in_(['confirmed', 'processing', 'done']),
         'required': Eval('state') == 'quotation',
@@ -24,7 +21,8 @@ class Sale(metaclass=PoolMeta):
     __name__ = 'sale.sale'
     cost = fields.Function(fields.Numeric('Sale Cost',
             digits=(16,2)), 'get_sale_cost')
-
+    profit_amount = fields.Function(fields.Numeric('Profit Amount',
+            digits=(16,2)), 'get_profit_amount')
 
     def get_sale_cost(self, name=None):
         res = []
@@ -35,6 +33,10 @@ class Sale(metaclass=PoolMeta):
             res.append((line.product.template.cost_price + expense) * Decimal(line.quantity))
         return sum(res)
 
+    def get_profit_amount(self, name=None):
+        res = self.total_amount - self.get_sale_cost()
+        return res
+
 
 class SaleProfitJournalStart(ModelView):
     'Sale Profit Journal Start'
@@ -76,8 +78,8 @@ class SaleProfitJournalReport(Report):
     __name__ = 'sale_cost.profit_journal_report'
 
     @classmethod
-    def get_context(cls, records, data):
-        report_context = super(SaleProfitJournalReport, cls).get_context(records, data)
+    def get_context(cls, records, header, data):
+        report_context = super().get_context(records, header, data)
         pool = Pool()
         Sale = pool.get('sale.sale')
         Tax = pool.get('account.tax')
@@ -91,7 +93,6 @@ class SaleProfitJournalReport(Report):
             amount = line.amount
             return (line.amount if amount else _ZERO) + tax_amount
 
-
         total_profit = _ZERO
         sales = Sale.search([
             ('sale_date', '=', data['sale_date']),
@@ -103,9 +104,7 @@ class SaleProfitJournalReport(Report):
         tax_amount = []
         total_amount = []
         for sale in sales:
-            profit_amount = sale.total_amount - sale.get_sale_cost()
-            setattr(sale, 'profit_amount', profit_amount)
-            total_profit.append(profit_amount)
+            total_profit.append(sale.profit_amount)
             untaxed_amount.append(sale.untaxed_amount)
             tax_amount.append(sale.tax_amount)
             total_amount.append(sale.total_amount)
diff --git a/tryton.cfg b/tryton.cfg
index 92b7963..a96445e 100644
--- a/tryton.cfg
+++ b/tryton.cfg
@@ -1,5 +1,5 @@
 [tryton]
-version=5.0.0
+version=6.0.0
 depends:
     product
     sale