Get rid of numbers map, look it up directly from the array.

Also modify the keys for the dependency graph, use the hashed version of
the todo instead of its position.
The position may shift when deleting tasks, which affects the consistency
of the dependency graph.

TodoList.py

@@ -24,7 +24,6 @@ class TodoList(object):
         The string will be parsed.
         """
         self._todos = []
-        self._numbers = {} # maintains todo -> number mapping
         self._depgraph = Graph.DirectedGraph()
 
         for string in p_todostrings:
@@ -46,6 +45,18 @@ class TodoList(object):
 
         return result
 
+    def todo_by_hash(self, p_hash):
+        """
+        Given the hash value of a todo, return the corresponding hash instance.
+        """
+
+        result = None
+        for todo in self._todos:
+            if hash(todo) == p_hash:
+                result = todo
+                break
+        return result
+
     def todo_by_dep_id(self, p_dep_id):
         """
         Returns the todo that has the id tag set to the value p_dep_id.
@@ -65,19 +76,19 @@ class TodoList(object):
         dep_id = p_todo.tag_value('id')
         # maintain dependency graph
         if dep_id:
-            self._depgraph.add_node(self.number(p_todo))
+            self._depgraph.add_node(hash(p_todo))
 
             # connect all tasks we have in memory so far that refer to this
             # task
             for dep in \
                 [dep for dep in self._todos if dep.has_tag('p', dep_id)]:
 
-                self._depgraph.add_edge(self.number(p_todo), self.number(dep), dep_id)
+                self._depgraph.add_edge(hash(p_todo), hash(dep), dep_id)
 
         for child in p_todo.tag_values('p'):
             parent = self.todo_by_dep_id(child)
             if parent:
-                self._depgraph.add_edge(self.number(parent), self.number(p_todo), child)
+                self._depgraph.add_edge(hash(parent), hash(p_todo), child)
 
     def add(self, p_src):
         """ Given a todo string, parse it and put it to the end of the list. """
@@ -105,7 +116,6 @@ class TodoList(object):
 
         Then there will be an edge 1 --> 2 with ID 4.
         """
-        self._numbers[p_todo] = len(self._todos) + 1
         self._todos.append(p_todo)
 
         self._maintain_dep_graph(p_todo)
@@ -124,7 +134,6 @@ class TodoList(object):
                 self.remove_dependency(self.number(parent), self.number(todo))
 
             del self._todos[p_number - 1]
-            del self._numbers[todo]
 
             self.dirty = True
 
@@ -189,9 +198,9 @@ class TodoList(object):
 
             return '%d' % new_id
 
-        if not self._depgraph.has_edge(p_number1, p_number2):
         from_todo = self.todo(p_number1)
         to_todo = self.todo(p_number2)
+        if not self._depgraph.has_edge(hash(from_todo), hash(to_todo)):
 
             if not from_todo or not to_todo:
                 return
@@ -204,7 +213,7 @@ class TodoList(object):
                 from_todo.set_tag('id', dep_id)
 
             to_todo.add_tag('p', dep_id)
-            self._depgraph.add_edge(p_number1, p_number2, dep_id)
+            self._depgraph.add_edge(hash(from_todo), hash(to_todo), dep_id)
             self._update_parent_cache()
             self.dirty = True
 
@@ -220,7 +229,7 @@ class TodoList(object):
 
         if dep_id:
             to_todo.remove_tag('p', dep_id)
-            self._depgraph.remove_edge(p_number1, p_number2)
+            self._depgraph.remove_edge(hash(from_todo), hash(to_todo))
             self._update_parent_cache()
 
             if not self.children(p_number1, True):
@@ -233,17 +242,19 @@ class TodoList(object):
         Returns a list of parent todos that (in)directly depend on the
         given todo.
         """
-        parents = self._depgraph.incoming_neighbors(p_number, not p_only_direct)
-        return [self.todo(parent) for parent in parents]
+        todo = self.todo(p_number)
+        parents = self._depgraph.incoming_neighbors(hash(todo), not p_only_direct)
+        return [self.todo_by_hash(parent) for parent in parents]
 
     def children(self, p_number, p_only_direct=False):
         """
         Returns a list of child todos that the given todo (in)directly depends
         on.
         """
+        todo = self.todo(p_number)
         children = \
-            self._depgraph.outgoing_neighbors(p_number, not p_only_direct)
-        return [self.todo(child) for child in children]
+            self._depgraph.outgoing_neighbors(hash(todo), not p_only_direct)
+        return [self.todo_by_hash(child) for child in children]
 
     def clean_dependencies(self):
         """
@@ -293,7 +304,7 @@ class TodoList(object):
         self.dirty = True
 
     def number(self, p_todo):
-        return self._numbers[p_todo]
+        return self._todos.index(p_todo) + 1
 
     def pp_number(self):
         """