即使列表未传递给函数，函数也会更改列表中的值

Question

我正在尝试实施 I.A。类似广度优先搜索的算法来解决 Water Jugs 问题，但我遇到了这个问题：

每次我向数组中添加一个新元素时，它都会将数组中的所有元素更改为类似它。

换句话说...

"frontier" 数组在每次 "jug" 函数调用之间更改其中的所有元素。

有人可以分享一些关于这段代码的见解吗？

（我比较担心实现逻辑，所以没有优化）

代码：

J1SIZE = 3
J2SIZE = 4

frontier = []
explored = []


def IsEmpty(array):
    result = False
    if len(array) == 0:
        result = True
    return result


#Fill up a jug
def fillJug(tempNode, jug):
    copyNode = tempNode
    copyNode = copyNode
    if jug == 1:
        copyNode[0] = J1SIZE
    elif jug == 2:
        copyNode[1] = J2SIZE
    print(copyNode)
    return copyNode

#Empty a jug
def emptyJug(tempNode, jug):
    copyNode = tempNode
    if jug == 1:
        copyNode[0] = 0
    elif jug == 2:
        copyNode[1] = 0
    print(copyNode)
    return copyNode

#Pass the content of a jug to another
def passJug(tempNode, jug):
    copyNode = tempNode
    if jug == 1:
        copyNode[1] = copyNode.j1
        copyNode[0] = 0
        if copyNode[1] > J2SIZE:
            copyNode[1] = J2SIZE
    elif jug == 2:
        copyNode[0] = copyNode[1]
        copyNode[1] = 0
        if copyNode[0] > J1SIZE:
            copyNode[0] = J1SIZE
    print(copyNode)
    return copyNode

#Check if solution was found
def goalTest(goalNode,currentNode):
    result = False
    if goalNode == currentNode:
        result = True
    return result

def BFS(start,end,frontier,explored):

    start_node = start
    frontier = [start_node] + frontier

    if goalTest(end,(frontier[0])):
        print('Solution:', frontier[0])
        exit()

    #Loop start
    while IsEmpty(frontier) == False:

        tempNode = frontier.pop(0)

        #Generate nodes (states)
        if tempNode[0] < J1SIZE:
            newNode = fillJug(tempNode, 1)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier1: ', frontier)

        if tempNode[1] < J2SIZE:
            newNode = fillJug(tempNode, 2)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier2: ', frontier)

        if tempNode[0] == J1SIZE:
            newNode = emptyJug(tempNode, 1)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier3: ', frontier)

        if tempNode[1] == J2SIZE:
            newNode = emptyJug(tempNode, 2)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier4: ', frontier)

        if (tempNode[0] > 0) and (tempNode[1] < J2SIZE):
            newNode = passJug(tempNode, 1)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier5: ', frontier)

        if (tempNode[1] > 0) and (tempNode[0] < J1SIZE):
            new_node = passJug(tempNode, 2)
            if new_node not in explored:
                frontier = [new_node] + frontier
                print('Frontier6: ', frontier)

        print('Frontier: ', frontier)
        print('Explored: ', explored)

        for node in frontier:
            if goalTest(end, node):
                print('Solution:', frontier[0])
                exit()
            if node not in explored:
                explored = [node] + explored

BFS([0,0],[0,2],frontier,explored)

固定码：

http://codepaste.net/auun4u

Answer 1

我制作了一个更小的代码示例来重现您的错误：

J1SIZE = 3
J2SIZE = 4


def fillJug(tempNode, jug):
    copyNode = tempNode
    copyNode = copyNode
    if jug == 1:
        copyNode[0] = J1SIZE
    elif jug == 2:
        copyNode[1] = J2SIZE
    return copyNode


frontier = [[0, 0]]
tempNode = frontier.pop(0)

newNode = fillJug(tempNode, 1)
frontier = [newNode] + frontier  # (1)

newNode = fillJug(tempNode, 2)  # (2)
frontier = [newNode] + frontier

问题在于，在我标记为 (1) 的行中，您正在设置 newNode，它指的是与 tempNode 相同的对象作为 frontier。然后，在我标记为 (2) 的行中，您正在更改 tempNode -- 在 fillJug 内。因此 frontier 中的值发生变化。具体来说，您让 copyNode 引用与 tempNode 相同的对象，然后您正在更改 copyNode（和 tempNode）引用的数据。

您应该将 copyNode 重新定义为

copyNode = tempNode[:]

这将导致 copyNode 和 tempNode 引用内存中的不同对象（具有相同的值）。（另一种选择是在导入 copy 后将 copyNode 设置为 copy.copy(tempNode)。）

所以新的 fillJug 将是

def fillJug(tempNode, jug):
    copyNode = tempNode[:]
    if jug == 1:
        copyNode[0] = J1SIZE
    elif jug == 2:
        copyNode[1] = J2SIZE
    return copyNode

同样的修复适用于其他 Jug 函数。

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