为什么坐标变量在Python中的函数中没有递增和递减呢？

Question

我正在用Python编写一个基于文本的冒险游戏，玩家在5x5网格上移动并拾取物品，但是我在更改玩家的坐标时遇到了问题。 coorx和coory在各自的功能范围内没有递增和递减。你知道吗

coorx = 3 #The beginning x coordinate of the player
coory = 3 #The beginning y coordinate of the player

loop = True
#The dimensions of the map are 5x5.
# __ __ __ __ __
#|  |  |  |  |  |
#|__|__|__|__|__|
#|  |  |  |  |  |
#|__|__|__|__|__|
#|  |  |><|  |  |
#|__|__|__|__|__|
#|  |  |  |  |  |
#|__|__|__|__|__|
#|  |  |  |  |  |
#|__|__|__|__|__|
#>< = The player's starting position on the map

def left(coorx):
    if coorx != 1: #This checks if the x co-ordinate is not less than 1 so the player does walk off the map.
        coorx -= 1 #This function moves the player left by decrementing the x co-ordinate.

def right(coorx):
    if coorx != 5: #This checks if the x co-ordinate is not more than 5 so the player does walk off the map.
        coorx += 1 #This function moves the player right by incrementing the x co-ordinate.

def back(coory):
    if coory != 1: #This checks if the y co-ordinate is not less than 1 so the player does walk off the map.
        coory -= 1 #This function moves the player left by decrementing the y co-ordinate.

def forward(coory):
    if coory != 5: #This checks if the y co-ordinate is not more than 5 so the player does walk off the map.
        coory += 1 #This function moves the player right by incrementing the y co-ordinate.


while loop: #This loops as long as the variable "loop" is True, and since "loop" never changes, this is an infinite loop.
    move = input().lower()

    if move == "l":
        left(coorx)
        print("You move left.")
        print(coorx, coory)
    elif move == "r":
        right(coorx)
        print("You move right.")
        print(coorx, coory)
    elif move == "f":
        forward(coory)
        print("You move forward.")
        print(coorx, coory)
    elif move == "b":
        back(coory)
        print("You move backwards.")
        print(coorx, coory)

这就是输出。你知道吗

>f
>You move forward.
>3 3
>f
>You move forward.
>3 3
>l
>You move left.
>3 3
>l
>You move left.
>3 3
>b
>You move backwards.
>3 3
>b
>You move backwards.
>3 3
>r
>You move right.
>3 3
>r
>You move right.
>3 3

如您所见，坐标始终不会从“3”变为“3”。如果您能帮我解决这个问题，我们将不胜感激。你知道吗

Answer 1

您的变量正在局部更改。使用全局解决问题。您还可以使用参数和返回坐标来解决问题。你知道吗

Answer 2

读一些让我想起这个问题的东西。无需return值或使用global即可更改坐标的一种方法是使用可变容器类型：

>>> coor = [3, 3]  # x, y
>>>
>>> def left():
...     if coor[0] != 1:
...         coor[0] -= 1
...
>>>
>>> left()
>>> coor
[2, 3]
>>>

这里发生的是变量coor只被引用，而不是赋值给。您要分配给的是容器中的，而不是变量coor本身。当全局coor在left()中没有赋值给同一个函数时，它使用了它的隐式存在性。你知道吗

（我想这就是我在first version of my previous answer中的想法。）

这也适用于字典，可读性更强：

>>> coor = dict(x=3, y=3)
>>>
>>> def left():
...     if coor['x'] != 1:
...         coor['x'] -= 1
...
>>>
>>> left()
>>> coor
{'x': 2, 'y': 3}
>>>

Answer 3

你的坐标是global，但是你没有声明它们是全局的，所以它们被一个同名的局部变量所遮蔽。您需要用函数声明它们global，以便能够修改它们。你知道吗

选项一（不带全局变量）：

def left(x_coord):
    if x_coord != 1: 
        x_coord -= 1
    return x_coord # Do something with this

方案二：

def left():
    global coorx
    if coorx != 1:
        coorx -= 1

您可以阅读有关globalshere和here的更多信息