cleaned up some comments; added a missing annotation

Author: davecom

Chapter3/queens.py

@@ -23,8 +23,10 @@ def __init__(self, columns: List[int]) -> None:
         self.columns: List[int] = columns
 
     def satisfied(self, assignment: Dict[int, int]) -> bool:
-        for q1c, q1r in assignment.items(): # q1c = queen 1 column, q1r = queen 1 row
-            for q2c in range(q1c + 1, len(self.columns) + 1): # q2c = queen 2 column
+        # q1c = queen 1 column, q1r = queen 1 row
+        for q1c, q1r in assignment.items():
+            # q2c = queen 2 column
+            for q2c in range(q1c + 1, len(self.columns) + 1):
                 if q2c in assignment:
                     q2r: int = assignment[q2c] # q2r = queen 2 row
                     if q1r == q2r: # same row?

Chapter4/dijkstra.py

@@ -38,7 +38,8 @@ def __eq__(self, other: DijkstraNode) -> bool:
 
 def dijkstra(wg: WeightedGraph[V], root: V) -> Tuple[List[Optional[float]], Dict[int, WeightedEdge]]:
     first: int = wg.index_of(root) # find starting index
-    distances: List[Optional[float]] = [None] * wg.vertex_count # distances are unknown at first
+    # distances are unknown at first
+    distances: List[Optional[float]] = [None] * wg.vertex_count
     distances[first] = 0 # the root is 0 away from the root
     path_dict: Dict[int, WeightedEdge] = {} # how we got to each vertex
     pq: PriorityQueue[DijkstraNode] = PriorityQueue()
@@ -47,12 +48,18 @@ def dijkstra(wg: WeightedGraph[V], root: V) -> Tuple[List[Optional[float]], Dict
     while not pq.empty:
         u: int = pq.pop().vertex # explore the next closest vertex
         dist_u: float = distances[u] # should already have seen it
-        for we in wg.edges_for_index(u): # look at every edge/vertex from the vertex in question
-            dist_v: float = distances[we.v] # the old distance to this vertex
-            if dist_v is None or dist_v > we.weight + dist_u: # no old distance or found shorter path
-                distances[we.v] = we.weight + dist_u # update distance to this vertex
-                path_dict[we.v] = we # update the edge on the shortest path to this vertex
-                pq.push(DijkstraNode(we.v, we.weight + dist_u)) # explore it soon
+        # look at every edge/vertex from the vertex in question
+        for we in wg.edges_for_index(u):
+            # the old distance to this vertex
+            dist_v: float = distances[we.v]
+            # no old distance or found shorter path
+            if dist_v is None or dist_v > we.weight + dist_u:
+                # update distance to this vertex
+                distances[we.v] = we.weight + dist_u
+                # update the edge on the shortest path to this vertex
+                path_dict[we.v] = we
+                # explore it soon
+                pq.push(DijkstraNode(we.v, we.weight + dist_u))
 
     return distances, path_dict
 

Chapter4/mst.py

@@ -35,7 +35,8 @@ def mst(wg: WeightedGraph[V], start: int = 0) -> Optional[WeightedPath]:
 
     def visit(index: int):
         visited[index] = True # mark as visited
-        for edge in wg.edges_for_index(index): # add all edges coming from here to pq
+        for edge in wg.edges_for_index(index):
+            # add all edges coming from here to pq
             if not visited[edge.v]:
                 pq.push(edge)
 
@@ -45,7 +46,8 @@ def visit(index: int):
         edge = pq.pop()
         if visited[edge.v]:
             continue # don't ever revisit
-        result.append(edge) # this is the current smallest, so add it to solution
+        # this is the current smallest, so add it to solution
+        result.append(edge)
         visit(edge.v) # visit where this connects
 
     return result

Chapter4/priority_queue.py

@@ -29,7 +29,7 @@ def empty(self) -> bool:
         return not self._container  # not is true for empty container
 
     def push(self, item: T) -> None:
-        heappush(self._container, item)  # priority determined by order of item
+        heappush(self._container, item)  # in by priority
 
     def pop(self) -> T:
         return heappop(self._container)  # out by priority

Chapter4/weighted_edge.py

@@ -26,7 +26,7 @@ def reversed(self) -> WeightedEdge:
         return WeightedEdge(self.v, self.u, self.weight)
 
     # so that we can order edges by weight to find the minimum weight edge
-    def __lt__(self, other: WeightedEdge):
+    def __lt__(self, other: WeightedEdge) -> bool:
         return self.weight < other.weight
 
     def __str__(self) -> str: