Let TodoList throw an exception when invalid todos are requested.

AddCommand.py

@@ -7,6 +7,7 @@ import Config
 import Command
 from PrettyPrinter import pretty_print
 from RelativeDate import relative_date_to_date
+import TodoList
 
 class AddCommand(Command.Command):
     def __init__(self, p_args, p_todolist,
@@ -46,14 +47,15 @@ class AddCommand(Command.Command):
                 try:
                     value = int(raw_value)
                     dep = self.todolist.todo(value)
-                except ValueError:
-                    continue
 
-                if dep:
                     if p_tag == 'after':
                         self.todolist.add_dependency(self.todo, dep)
                     elif p_tag == 'before' or p_tag == 'partof':
                         self.todolist.add_dependency(dep, self.todo)
+                except ValueError:
+                    continue
+                except TodoList.InvalidTodoException:
+                    pass
 
                 self.todo.remove_tag(p_tag, raw_value)
 

AppendCommand.py

 import Command
 from PrettyPrinter import pretty_print
+import TodoList
 from Utils import convert_todo_number
 
 class AppendCommand(Command.Command):
@@ -16,11 +17,11 @@ class AppendCommand(Command.Command):
             text = " ".join(self.args[1:])
 
             if number and text:
-                todo = self.todolist.todo(number)
-                if todo:
+                try:
+                    todo = self.todolist.todo(number)
                     self.todolist.append(todo, text)
                     self.out(pretty_print(todo, [self.todolist.pp_number()]))
-                else:
+                except TodoList.InvalidTodoException:
                     self.error("Invalid todo number given.")
             else:
                 self.error(self.usage())

TodoList.py

@@ -9,6 +9,9 @@ from PrettyPrinter import pretty_print_list
 import Todo
 import View
 
+class InvalidTodoException(Exception):
+    pass
+
 class TodoList(object):
     """
     Provides operations for a todo list, such as adding items, removing them,
@@ -41,7 +44,7 @@ class TodoList(object):
         try:
             result = self._todos[p_number - 1]
         except IndexError:
-            result = None
+            raise InvalidTodoException
 
         return result
 
@@ -284,7 +287,10 @@ class TodoList(object):
         self.dirty = True
 
     def number(self, p_todo):
-        return self._todos.index(p_todo) + 1
+        try:
+            return self._todos.index(p_todo) + 1
+        except ValueError:
+            raise InvalidTodoException
 
     def pp_number(self):
         """

test/TodoListTest.py

@@ -78,7 +78,7 @@ class TodoListTester(unittest.TestCase):
             "(C) Baz @Context1 +Project1 key:value")
         self.assertEquals(self.todolist.count(), count - 1)
         self.assertTrue(self.todolist.is_dirty())
-        self.assertRaises(ValueError, self.todolist.number, todo)
+        self.assertRaises(TodoList.InvalidTodoException, self.todolist.number, todo)
 
     def test_append1(self):
         todo = self.todolist.todo(3)
@@ -108,9 +108,8 @@ class TodoListTester(unittest.TestCase):
 
     def test_todo(self):
         count = self.todolist.count()
-        todo = self.todolist.todo(count+100)
 
-        self.assertEquals(todo, None)
+        self.assertRaises(TodoList.InvalidTodoException, self.todolist.todo, count + 100)
         self.assertFalse(self.todolist.is_dirty())
 
     def test_string(self):
@@ -139,7 +138,7 @@ class TodoListTester(unittest.TestCase):
 
     def test_todo_number2(self):
         todo = Todo.Todo("Non-existent")
-        self.assertRaises(ValueError, self.todolist.number, todo)
+        self.assertRaises(TodoList.InvalidTodoException, self.todolist.number, todo)
 
     def test_todo_complete(self):
         todo = self.todolist.todo(1)