diff env/lib/python3.9/site-packages/networkx/algorithms/shortest_paths/astar.py @ 0:4f3585e2f14b draft default tip

"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.9/site-packages/networkx/algorithms/shortest_paths/astar.py	Mon Mar 22 18:12:50 2021 +0000
@@ -0,0 +1,176 @@
+"""Shortest paths and path lengths using the A* ("A star") algorithm.
+"""
+from heapq import heappush, heappop
+from itertools import count
+
+import networkx as nx
+from networkx.algorithms.shortest_paths.weighted import _weight_function
+
+__all__ = ["astar_path", "astar_path_length"]
+
+
+def astar_path(G, source, target, heuristic=None, weight="weight"):
+    """Returns a list of nodes in a shortest path between source and target
+    using the A* ("A-star") algorithm.
+
+    There may be more than one shortest path.  This returns only one.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+       Starting node for path
+
+    target : node
+       Ending node for path
+
+    heuristic : function
+       A function to evaluate the estimate of the distance
+       from the a node to the target.  The function takes
+       two nodes arguments and must return a number.
+
+    weight : string or function
+       If this is a string, then edge weights will be accessed via the
+       edge attribute with this key (that is, the weight of the edge
+       joining `u` to `v` will be ``G.edges[u, v][weight]``). If no
+       such edge attribute exists, the weight of the edge is assumed to
+       be one.
+       If this is a function, the weight of an edge is the value
+       returned by the function. The function must accept exactly three
+       positional arguments: the two endpoints of an edge and the
+       dictionary of edge attributes for that edge. The function must
+       return a number.
+
+    Raises
+    ------
+    NetworkXNoPath
+        If no path exists between source and target.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> print(nx.astar_path(G, 0, 4))
+    [0, 1, 2, 3, 4]
+    >>> G = nx.grid_graph(dim=[3, 3])  # nodes are two-tuples (x,y)
+    >>> nx.set_edge_attributes(G, {e: e[1][0] * 2 for e in G.edges()}, "cost")
+    >>> def dist(a, b):
+    ...     (x1, y1) = a
+    ...     (x2, y2) = b
+    ...     return ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
+    >>> print(nx.astar_path(G, (0, 0), (2, 2), heuristic=dist, weight="cost"))
+    [(0, 0), (0, 1), (0, 2), (1, 2), (2, 2)]
+
+
+    See Also
+    --------
+    shortest_path, dijkstra_path
+
+    """
+    if source not in G or target not in G:
+        msg = f"Either source {source} or target {target} is not in G"
+        raise nx.NodeNotFound(msg)
+
+    if heuristic is None:
+        # The default heuristic is h=0 - same as Dijkstra's algorithm
+        def heuristic(u, v):
+            return 0
+
+    push = heappush
+    pop = heappop
+    weight = _weight_function(G, weight)
+
+    # The queue stores priority, node, cost to reach, and parent.
+    # Uses Python heapq to keep in priority order.
+    # Add a counter to the queue to prevent the underlying heap from
+    # attempting to compare the nodes themselves. The hash breaks ties in the
+    # priority and is guaranteed unique for all nodes in the graph.
+    c = count()
+    queue = [(0, next(c), source, 0, None)]
+
+    # Maps enqueued nodes to distance of discovered paths and the
+    # computed heuristics to target. We avoid computing the heuristics
+    # more than once and inserting the node into the queue too many times.
+    enqueued = {}
+    # Maps explored nodes to parent closest to the source.
+    explored = {}
+
+    while queue:
+        # Pop the smallest item from queue.
+        _, __, curnode, dist, parent = pop(queue)
+
+        if curnode == target:
+            path = [curnode]
+            node = parent
+            while node is not None:
+                path.append(node)
+                node = explored[node]
+            path.reverse()
+            return path
+
+        if curnode in explored:
+            # Do not override the parent of starting node
+            if explored[curnode] is None:
+                continue
+
+            # Skip bad paths that were enqueued before finding a better one
+            qcost, h = enqueued[curnode]
+            if qcost < dist:
+                continue
+
+        explored[curnode] = parent
+
+        for neighbor, w in G[curnode].items():
+            ncost = dist + weight(curnode, neighbor, w)
+            if neighbor in enqueued:
+                qcost, h = enqueued[neighbor]
+                # if qcost <= ncost, a less costly path from the
+                # neighbor to the source was already determined.
+                # Therefore, we won't attempt to push this neighbor
+                # to the queue
+                if qcost <= ncost:
+                    continue
+            else:
+                h = heuristic(neighbor, target)
+            enqueued[neighbor] = ncost, h
+            push(queue, (ncost + h, next(c), neighbor, ncost, curnode))
+
+    raise nx.NetworkXNoPath(f"Node {target} not reachable from {source}")
+
+
+def astar_path_length(G, source, target, heuristic=None, weight="weight"):
+    """Returns the length of the shortest path between source and target using
+    the A* ("A-star") algorithm.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+       Starting node for path
+
+    target : node
+       Ending node for path
+
+    heuristic : function
+       A function to evaluate the estimate of the distance
+       from the a node to the target.  The function takes
+       two nodes arguments and must return a number.
+
+    Raises
+    ------
+    NetworkXNoPath
+        If no path exists between source and target.
+
+    See Also
+    --------
+    astar_path
+
+    """
+    if source not in G or target not in G:
+        msg = f"Either source {source} or target {target} is not in G"
+        raise nx.NodeNotFound(msg)
+
+    weight = _weight_function(G, weight)
+    path = astar_path(G, source, target, heuristic, weight)
+    return sum(weight(u, v, G[u][v]) for u, v in zip(path[:-1], path[1:]))