Added base class for PathFinder, fixed typing errors

python/pathfinding_demo.py

@@ -8,7 +8,8 @@
 import matplotlib.pyplot as plt
 import numpy as np
 import time
-from typing import Protocol, Optional
+from typing import Optional
+from abc import ABC, abstractmethod
 
 #
 # Type and interfaces definition
@@ -16,15 +17,13 @@ from typing import Protocol, Optional
 
 type Point2D = tuple[int, int] # tuple(x, y)
 type Path = list[Point2D]
-type ElapsedTime_ns = int # nanoseconds
-type VisitedNodeCount = int
 
 class Map:
     """
     2D map consisting of cells with given cost
     """
     # array not defined as private, as plotting utilities work with it directly
-    array: np.array
+    array: np.ndarray
     _visited_nodes: int
 
     def __init__(self, width: int, height: int) -> None:
@@ -60,6 +59,14 @@ class Map:
                     points.append(p)
         return points
     
+    def GetPointCost(self, point: Point2D) -> float:
+        x, y = point
+        row, col = y, x
+        return self.array[(row, col)]
+    
+    def GetPathCost(self, path: Path) -> float:
+        return sum([self.GetPointCost(p) for p in path])
+
     def ResetVisitedCount(self) -> None:
         self._visited_nodes = 0
 
@@ -68,32 +75,12 @@ class Map:
 
     def Visit(self, point: Point2D) -> float:
         """
-        Visit the node, returning its cost
+        Visit the node and return its cost
         """
         if not self.IsPointValid(point):
             raise ValueError("Point out of bounds")
         self._visited_nodes += 1
-        x, y = point
-        row, col = y, x
-        return self.array[(row, col)]
-
-
-class PathFinder(Protocol):
-    def SetMap(m: Map) -> None:
-        ...
-
-    def CalculatePath(start: Point2D, end: Point2D) -> Path:
-        """
-        Calculate path on a given map.
-        Note: map must be set first using SetMap (or using constructor)
-        """
-
-    def GetStats() -> (ElapsedTime_ns, VisitedNodeCount):
-        """
-        Return performance stats for the last calculation:
-        - elapsed time in nanoseconds,
-        - number of visited nodes during search
-        """
+        return self.GetPointCost(point)
 
 #
 # Drawing utilities
@@ -129,50 +116,68 @@ class Visualizer:
         self._axes.plot(xs[-1], ys[-1], 'o', color='magenta', markersize=8)  # end point
 
 #
-# Method: depth-first search
+# Pathfinding implementations
 #
 
-class DFS:
-
-    name = "Depth First Search"
+class PathFinderBase(ABC):
+    name: str
     _map: Optional[Map]
     _elapsed_time_ns: int
     _visited_node_count: int
 
     def __init__(self) -> None:
         self._map = None
+        self._elapsed_time_ns = 0
+        self._visited_node_count = 0
+
 
     def SetMap(self, m: Map) -> None:
         self._map = m
 
-    def CalculatePath(self, start: Point2D, end: Point2D) -> Path:
+    def CalculatePath(self, start: Point2D, end: Point2D) -> Optional[Path]:
+        """
+        Calculate path on a given map.
+        Note: map must be set first using SetMap
+        """
         assert self._map is not None, "SetMap must be called first"
         self._map.ResetVisitedCount()
         start_time = time.perf_counter_ns()
-
         res = self._CalculatePath(start, end)
-        print(f"{res=}")
-
         stop_time = time.perf_counter_ns()
         self._elapsed_time_ns = stop_time - start_time
         self._visited_node_count = self._map.GetVisitedCount()
         return res
 
-    def GetStats(self) -> (ElapsedTime_ns, VisitedNodeCount):
+    @abstractmethod
+    def _CalculatePath(self, start: Point2D, end: Point2D) -> Optional[Path]:
+        """
+        This method must be implemented by the derived classes
+        """
+
+    def GetStats(self) -> tuple[int, int]:
+        """
+        Return performance stats for the last calculation:
+        - elapsed time in nanoseconds,
+        - number of visited nodes during search
+        """
         return self._elapsed_time_ns, self._visited_node_count
 
+
+class DFS(PathFinderBase):
+
+    name = "Depth First Search"
+
     def _CalculatePath(self, 
                        point: Point2D,
                        end_point: Point2D,
                        path: Optional[list[Point2D]] = None,
                        visited: Optional[set[Point2D]] = None) -> Optional[Path]:
-        """
-        Find (any) path, not guaranteed to be optimal (and it most probably won't be)
-        """
         if visited is None:
             visited = set()
         if path is None:
             path = list()
+        if self._map is None:
+            return None # to make mypy happy
         # We don't need to know cost in this case, but we still want to track
         # how many nodes we've visited
         _ = self._map.Visit(point) 
@@ -198,12 +203,12 @@ def main():
     # Define the map and start/stop points
     m = Map(15,10)
     m.Randomize()
-    starting_point: Point2D = (0,9)
-    end_point: Point2D = (14,1)
+    starting_point: Point2D = (14,1)
+    end_point: Point2D = (0,9)
 
-    path_finder_classes: list[PathFinder] = {
+    path_finder_classes: list[type[PathFinderBase]] = [
         DFS,
-    }
+    ]
 
     v = Visualizer()
     v.DrawMap(m)
@@ -213,8 +218,12 @@ def main():
         path_finder.SetMap(m)
         path = path_finder.CalculatePath(starting_point, end_point)
         elapsed_time, visited_nodes = path_finder.GetStats()
-        print(f"{path_finder.name:22}: took {elapsed_time/1e6} ms, visited {visited_nodes} nodes")
-        v.DrawPath(path)
+        if path is not None: 
+            cost = m.GetPathCost(path)
+            print(f"{path_finder.name:22}: took {elapsed_time/1e6:.3f} ms, visited {visited_nodes} nodes, cost {cost:.2f}")
+            v.DrawPath(path)
+        else:
+            print(f"{path_finder.name}: No path found")
 
     plt.show()