Use PySON

service.py

@@ -3,13 +3,14 @@
 "Service"
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.model.cacheable import Cacheable
+from trytond.pyson import Eval
 
 
 class Employee(ModelSQL, ModelView, Cacheable):
     _name = 'company.employee'
 
     cost_price = fields.Function('get_cost_price', string='Cost Price',
-            type='numeric', digits="(16, currency_digits)",
+            type='numeric', digits=(16, Eval('currency_digits', 2)),
             depends=['currency_digits'],
             help="Hourly cost price for this Employee")
     cost_prices = fields.One2Many('company.employee_cost_price', 'employee',
@@ -99,7 +100,8 @@ class EmployeeCostPrice(ModelSQL, ModelView):
     _description = __doc__
     _rec_name = 'date'
     date = fields.Date('Date', required=True, select=1)
-    cost_price = fields.Numeric('Cost Price', digits="(16, currency_digits)",
+    cost_price = fields.Numeric('Cost Price',
+            digits=(16, Eval('currency_digits', 2)),
             required=True, depends=['currency_digits'],
             help="Hourly cost price")
     employee = fields.Many2One('company.employee', 'Employee')

work.py

@@ -2,6 +2,7 @@
 #this repository contains the full copyright notices and license terms.
 
 from trytond.model import ModelView, ModelSQL, fields
+from trytond.pyson import Not, Equal, Eval
 from decimal import Decimal
 
 class TimesheetLine(ModelSQL, ModelView):
@@ -33,20 +34,23 @@ class Work(ModelSQL, ModelView):
 
     product = fields.Many2One('product.product', 'Product',
             states={
-                'invisible': "type!= 'task'"
+                'invisible': Not(Equal(Eval('type'), 'task')),
             }, on_change=['product', 'party', 'hours', 'company'],
             depends=['type', 'party', 'hours', 'company'])
-    list_price = fields.Numeric('List Price', digits="(16, currency_digits)",
+    list_price = fields.Numeric('List Price',
+            digits=(16, Eval('currency_digits', 2)),
             states={
-                'invisible': "type!= 'task'"
+                'invisible': Not(Equal(Eval('type'), 'task')),
             }, depends=['type', 'currency_digits'])
     revenue = fields.Function('get_revenue', type='numeric',
-            string='Revenue', digits="(16, currency_digits)",
+            string='Revenue',
+            digits=(16, Eval('currency_digits', 2)),
             states={
-                'invisible': "type!= 'project'"
+                'invisible': Not(Equal(Eval('type'), 'project')),
             }, depends=['type', 'currency_digits'])
     cost = fields.Function('get_cost', string='Cost', type='numeric',
-            digits="(16, currency_digits)", depends=['currency_digits'])
+            digits=(16, Eval('currency_digits', 2)),
+            depends=['currency_digits'])
     currency_digits = fields.Function('get_currency_digits', type='integer',
             string='Currency Digits', on_change_with=['company'])