Fixes for setting priority and completion.

When setting a priority, a task may not be completed.
When a todo is completed, set priority to None.

TodoBase.py

@@ -107,7 +107,9 @@ class TodoBase(object):
         Priority remains unchanged when an invalid priority is given.
         """
 
-        if p_priority == None or re.match('^[A-Z]$', p_priority):
+        if not self.is_completed() and \
+            (p_priority == None or re.match('^[A-Z]$', p_priority)):
+
             self.fields['priority'] = p_priority
 
             priority_str = '' if p_priority == None else '(' + p_priority + ') '
@@ -152,7 +154,9 @@ class TodoBase(object):
         Marks the todo as complete.
         Sets the completed flag and sets the completion date to today.
         """
-        if not self.fields['completed']:
+        if not self.is_completed():
+            self.set_priority(None)
+
             self.fields['completed'] = True
             today = datetime.date.today()
             self.fields['completionDate'] = today

test/TodoBaseTest.py

@@ -109,6 +109,14 @@ class TodoBaseTester(unittest.TestCase):
         self.assertEquals(todo.priority(), None)
         self.assertTrue(re.match(r'^Foo$', todo.src))
 
+    def test_set_priority6(self):
+        """ Do not set priorities on completed tasks. """
+        todo = TodoBase.TodoBase("x 2014-06-13 Foo")
+        todo.set_priority('A')
+
+        self.assertFalse(todo.priority())
+        self.assertEquals(todo.src, "x 2014-06-13 Foo")
+
     def test_project1(self):
         todo = TodoBase.TodoBase("(C) Foo +Bar +Baz")
 
@@ -152,6 +160,7 @@ class TodoBaseTester(unittest.TestCase):
         today = datetime.date.today()
         today_str = today.isoformat()
 
+        self.assertFalse(todo.priority())
         self.assertEquals(todo.fields['completionDate'], today)
         self.assertTrue(re.match('^x ' + today_str + ' Foo', todo.src))