fixes #1

invoice.py

@@ -5,8 +5,9 @@ from trytond.modules.product import price_digits
 from trytond.transaction import Transaction
 from trytond.pyson import If, Eval, Bool
 from trytond.exceptions import UserError
+from trytond.modules.account.tax import TaxableMixin
+
 
-    
 class InvoiceLine(metaclass=PoolMeta):
     'Invoice Line'
     __name__ = 'account.invoice.line'
@@ -26,7 +27,7 @@ class InvoiceLine(metaclass=PoolMeta):
     unit_price_days = fields.Numeric('Unit Price Days',
                                      digits=price_digits)
 
-
+    
     @property
     def taxable_lines(self):
         # In case we're called from an on_change we have to use some sensible
@@ -38,6 +39,7 @@ class InvoiceLine(metaclass=PoolMeta):
         else:
             invoice_type = getattr(self, 'invoice_type', None)
         if invoice_type == 'in':
+            unit_price = 'unit_price'
             if context.get('_deductible_rate') is not None:
                 deductible_rate = context['_deductible_rate']
             else:
@@ -48,14 +50,16 @@ class InvoiceLine(metaclass=PoolMeta):
                 return []
         else:
             deductible_rate = 1
+            unit_price = 'unit_price_days'
+            
         return [(
                 getattr(self, 'taxes', None) or [],
-                ((getattr(self, 'unit_price_days', None) or Decimal(0))
+                ((getattr(self, unit_price, None) or Decimal(0))
                     * deductible_rate),
                 getattr(self, 'quantity', None) or 0,
                 getattr(self, 'tax_date', None),
                 )]
-    
+
     @fields.depends('type', 'quantity', 'unit_price', 'invoice',
                     '_parent_invoice.currency', 'currency', 'rental_days',
                     'unit_price_days', 'invoice_type')