python - 结构类未定义尚未使用？

Question

这是来自 tkinter 游戏 Random 和 tkinter 模块的代码的一部分已被导入。我的问题是——

1. Struct 类只是初始化了，没有定义，只是简单的传递了，却被使用了。

def run(rows, cols):
# create the root and the canvas
global canvas
root = Tk()
margin = 5
cellSize = 15
canvasWidth = 2*margin + cols*cellSize
canvasHeight = 2*margin + rows*cellSize+100
canvas = Canvas(root, width=canvasWidth, height=canvasHeight)
canvas.pack()
# Store canvas in root and in canvas itself for callbacks
root.canvas = canvas.canvas = canvas
# Set up canvas data and call init
class Struct: pass
canvas.data = Struct()
canvas.data.margin = margin
canvas.data.cellSize = cellSize
canvas.data.canvasWidth = canvasWidth
canvas.data.canvasHeight = canvasHeight
canvas.data.rows = rows
canvas.data.cols = cols
canvas.data.canvasWidth = canvasWidth
canvas.data.canvasHeight = canvasHeight
canvas.data.player1Score = 0
canvas.data.player2Score = 0
canvas.data.inGame = False
init()
# set up events
root.bind("<Key>", keyPressed)
timerFired()
# and launch the app
root.mainloop()  # This call BLOCKS (so your program waits until you close the window!)
run(40,40)

2.这行代码中发生了什么：

root.canvas = canvas.canvas = canvas
class Struct: pass
canvas.data = Struct()

3. 由于没有定义类，canvas.data._______ 是如何使用的？

标签： pythonoop

Answer 1

问题：未定义的结构类尚未使用？

你错了，class Struct 是定义的。
此行定义了一个有效对象：

class Struct: pass

下面两个例子是等价的！

1. 空对象Struct成为canvas属性，然后用属性扩展对象。

   margin = 5
   
   # Define the object
   class Struct: pass
   
   # Instantiate the object `Struct` 
   # Assign the reference to the object `Struct` to the attribute `.data`
   canvas.data = Struct()
   
   # Assing the value `margin` to the attribute `.margin` of the object `Struct`
   canvas.data.margin = margin
   
   # Access the attribute `.margin` in the object `Struct`
   print(canvas.data.margin)
   # >>> 5
   

2. Struct使用预定义的对象class Struct.__init__

   margin = 5
   
   # Define the object
   class Struct:
       def __init__(self, margin):
           self.margin = margin
   
   # Instantiate the object `Struct` 
   # Pass the value `margin` to it
   # Assign the reference to the object `Struct` to the attribute `.data`
   canvas.data = Struct(margin)
   
   # Access the attribute `.margin` in the object `Struct`
   print(canvas.data.margin)
   # >>> 5