def check_neighbors(self, start, end, grid, open_list):
node = open_list.pop(0)
node.closed = True
if node == end:
return backtrace(end)
neighbors = self.find_neighbors(grid, node)
for neighbor in neighbors:
if neighbor.closed or neighbor.opened:
continue
open_list.append(neighbor)
neighbor.opened = True
neighbor.parent = node
def check_neighbors(self, start, end, grid, open_list):
node = open_list.pop(0)
node.closed = True
if node == end:
return backtrace(end)
neighbors = self.find_neighbors(grid, node)
for neighbor in neighbors:
if neighbor.closed or neighbor.opened:
continue
open_list.append(neighbor)
neighbor.opened = True
neighbor.parent = node
def check_neighbors(self,
start,
end,
grid,
open_list,
open_value=True,
backtrace_by=None,
width=0,
height=0):
"""
find next path segment based on given node
(or return path if we found the end)
"""
# pop node with minimum 'f' value
node = heapq.nsmallest(1, open_list)[0]
open_list.remove(node)
node.closed = True
width = grid.width
height = grid.height
# if reached the end position, construct the path and return it
# (ignored for bi-directional a*, there we look for a neighbor that is
# part of the oncoming path)
if not backtrace_by and node == end:
return backtrace(end)
# get neighbors of the current node
neighbors = self.find_neighbors(grid, node)
for neighbor in neighbors:
if neighbor.closed:
# already visited last minimum f value
continue
if backtrace_by and neighbor.opened == backtrace_by:
# found the oncoming path
if backtrace_by == BY_END:
return bi_backtrace(node, neighbor)
else:
return bi_backtrace(neighbor, node)
# check if the neighbor has not been inspected yet, or
# can be reached with smaller cost from the current node
self.process_node(neighbor, node, end, open_list, open_value,
width, height)
# the end has not been reached (yet) keep the find_path loop running
return None
def check_neighbors(self, start, end, grid, open_list,
open_value=True, backtrace_by=None):
"""
find next path segment based on given node
(or return path if we found the end)
"""
# pop node with minimum 'f' value
node = heapq.nsmallest(1, open_list)[0]
open_list.remove(node)
node.closed = True
# if reached the end position, construct the path and return it
# (ignored for bi-directional a*, there we look for a neighbor that is
# part of the oncoming path)
if not backtrace_by and node == end:
return backtrace(end)
# get neighbors of the current node
neighbors = self.find_neighbors(grid, node)
for neighbor in neighbors:
if neighbor.closed:
# already visited last minimum f value
continue
if backtrace_by and neighbor.opened == backtrace_by:
# found the oncoming path
if backtrace_by == BY_END:
return bi_backtrace(node, neighbor)
else:
return bi_backtrace(neighbor, node)
# check if the neighbor has not been inspected yet, or
# can be reached with smaller cost from the current node
self.process_node(neighbor, node, end, open_list, open_value)
# the end has not been reached (yet) keep the find_path loop running
return None
def find_path(self, start, end, grid, max_runs=MAX_RUNS):
"""
find a path from start to end node on grid using the A* algorithm
:param start: start node
:param end: end node
:param grid: grid that stores all possible steps/tiles as 2D-list
:param max_runs: max. amount of tries until we abort the search
(optional, only if we enter huge grids and have time constrains)
<=0 means there are no constrains and the code might run on any
large map.
:return:
"""
open_list = []
start.g = 0
start.f = 0
# push the start node into the open list
heapq.heappush(open_list, start)
runs = 0
# while the open list is not empty
while len(open_list) > 0:
runs += 1
if 0 < max_runs <= runs:
logging.error('A* run into barrier of {} iterations without '
'finding the destination'.format(max_runs))
break
# pop node with minimum 'f' value
node = heapq.nsmallest(1, open_list)[0]
open_list.remove(node)
node.closed = True
# if reached the end position, construct the path and return it
if node == end:
return backtrace(end), runs
# get neighbors of the current node
neighbors = grid.neighbors(node, self.diagonal_movement)
for neighbor in neighbors:
if neighbor.closed:
# already visited last minimum f value
continue
x = neighbor.x
y = neighbor.y
# get the distance between current node and the neighbor
ng = node.g
if x - node.x == 0 or y - node.y == 0:
# direct neighbor - distance is 1
ng += 1
else:
# not a direct neighbor - diagonal movement
ng += SQRT2
# check if the neighbor has not been inspected yet, or
# can be reached with smaller cost from the current node
if not neighbor.opened or ng < neighbor.g:
neighbor.g = ng
neighbor.h = neighbor.h or self.weight * \
self.heuristic(abs(x - end.x), abs(y - end.y))
# f is the estimated total cost from start to goal
neighbor.f = neighbor.g + neighbor.h
neighbor.parent = node
if not neighbor.opened:
heapq.heappush(open_list, neighbor)
neighbor.opened = True
else:
# the neighbor can be reached with smaller cost.
# Since its f value has been updated, we have to
# update its position in the open list
open_list.remove(neighbor)
heapq.heappush(open_list, neighbor)
# failed to find path
return [], runs