Problem with arrays in a recursive class function

[Bruno Desthuilliers]

Aaron Scott a écrit :
> I have a list of nodes, and I need to find a path from one node to
> another. The nodes each have a list of nodes they are connected to,
> set up like this:
> 
> 
> 
> class Node(object):
> 	def __init__(self, connectedNodes):
> 		self.connectedNodes = connectedNodes
> 
> nodes = {
> 	1: Node([4]),
> 	2: Node([3]),
> 	3: Node([2, 4, 5]),
> 	4: Node([1, 6, 3]),
> 	5: Node([3, 7]),
> 	6: Node([4, 9]),
> 	7: Node([5, 8]),
> 	8: Node([7, 9]),
> 	9: Node([6, 8])
> }
> 
> 
> 
> I made a quick brute-force pathfinder to solve it (in this case, a
> path from node 1 to node 9). Here it is:
> 
> 
> 
> class PathFind(object):
> 	def __init__(self, source, destination):
> 		self.source = source
> 		self.destination = destination
> 		self.solved = []
> 	def Search(self):
> 		self.PathFind([self.source])
 >
> 		if self.solved:
> 			print "Solutions: "
> 			for i in self.solved:
> 				print "\t" + str(i)

                                 print "\t%s" % i

> 		else:
> 			print "Couldn't solve."
> 	def PathFind(self, trail):
> 		location = trail[-1]
> 		if location == self.destination:
> 			self.solved.append(trail)

I think you want
                         self.solved.append(trail[:])

Hint : Python doesn't use "pass by value".


  > The problem is the array trail[], which seems to survive from instance
> to instance of PathFind(). I thought that by calling self.PathFind
> (trail[:]), I was creating a new copy of trail[], 

Yes. But on the 'not solved' branch, you do mutate trail !-)