属性错误：对象没有属性Python

Question

我正试图编写一个版本的康威的生活游戏，但是我一直收到这样一条消息：在请求引用nextState之前，它似乎应该声明它的值。这是我的代码：

from tkinter import *
root = Tk()

class Cell (Button):
    Dead = 0
    Live = 1

    def __init__ (self,parent):
        Button.__init__(self,parent, relief = "raised" , width = 2 , borderwidth = 1 , command = self.onpress)
        self.displayState(Cell.Dead)

    def onpress (self):
        if self.state == Cell.Live:
            self.displayState(Cell.Dead)
        elif self.state == Cell.Dead:
            self.displayState(Cell.Live)

    def setNextState (self , Neighbours):
        if self.state == Cell.Live and (Neighbours < 2 or Neighbours > 3):
            self.nextState = Cell.Dead
        elif self.state == Cell.Dead and Neighbours == 3:
            self.nextState = Cell.Live
        elif self.state == Cell.Dead and Neighbours != 3:
            self.nextState = self.state

    def stepToNextState(self):
        self.displayState(self.nextState)

    def displayState (self , newstate):
        self.state = newstate
        if self.state == Cell.Live:
            self["bg"] = "black"
        if self.state == Cell.Dead:
            self["bg"] = "white"

class Grid:
    def __init__(self,parent,sizex,sizey):
        self.sizex = sizex
        self.sizey = sizey
        self.cells = []
        for a in range (0,self.sizex):
            rowcells = []
            for b in range (0, self.sizey):
                c = Cell(parent)
                c.grid(row=b , column=a)
                rowcells.append(c)
            self.cells.append(rowcells)

    def step (self):
        cells = self.cells
        for x in range (0,self.sizex):
            if x==0: x_down = self.sizex-1
            else: x_down = x-1
            if x==self.sizex-1: x_up = 0
            else: x_up = x+1
            for y in range(0,self.sizey):
                if y==0: y_down = self.sizey-1
                else: Y_down = y-1
                if y==self.sizey-1: y_up = 0
                else: y_up = y+1
                sum = cells[x_down][y].state + cells[x_up][y].state + cells[x][y_down].state + cells[x][y_up].state + cells[x_down][y_down].state +cells[x_up][y_up].state + cells[x_down][y_up].state + cells[x_up][y_down].state
                cells[x][y].setNextState(sum)
            for row in cells:
                for cell in row:
                    cell.stepToNextState()

    def clear(self):
        for row in self.cells:
            for cell in row:
                cell.displayState(Cell.Dead)

if __name__ == "__main__":
    frame = Frame(root)
    frame.pack()
    grid = Grid(frame,25,25)
    bottomFrame = Frame(root)
    bottomFrame.pack (side = BOTTOM)
    buttonStep = Button(bottomFrame , text="Step" , command=grid.step)
    buttonStep.pack(side = LEFT)
    buttonClear = Button(bottomFrame, text = "Clear", command=grid.clear)
    buttonClear.pack(side=LEFT , after=buttonStep)
    root.mainloop()

错误消息是：

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python33\lib\tkinter\__init__.py", line 1442, in __call__
    return self.func(*args)
  File "C:\Users\Owner\Desktop\Other\Programs & Misc\Python\Tyler's Game of Life.py", line 65, in step
    cell.stepToNextState()
  File "C:\Users\Owner\Desktop\Other\Programs & Misc\Python\Tyler's Game of Life.py", line 27, in stepToNextState
    self.displayState(self.nextState)
AttributeError: 'Cell' object has no attribute 'nextState'

如果有人能指出错误发生的地方/造成错误的原因以及可能的解决方法，我将不胜感激。

Answer 1

问题似乎是您的for row in cells循环位于您以前的for x in range(0, self.sizex)循环内。如果您正确缩进step方法，它应该是这样的：

def step (self):
    cells = self.cells
    for x in range (0,self.sizex):
        if x==0: x_down = self.sizex-1
        else: x_down = x-1
        if x==self.sizex-1: x_up = 0
        else: x_up = x+1
        for y in range(0,self.sizey):
            if y==0: y_down = self.sizey-1
            else: Y_down = y-1
            if y==self.sizey-1: y_up = 0
            else: y_up = y+1
            sum = cells[x_down][y].state + cells[x_up][y].state + cells[x][y_down].state + cells[x][y_up].state + cells[x_down][y_down].state +cells[x_up][y_up].state + cells[x_down][y_up].state + cells[x_up][y_down].state
            cells[x][y].setNextState(sum)
    for row in cells:                     # unindent these
        for cell in row:                  # lines by one
            cell.stepToNextState()        # level each

如果所有的缩进问题都得到了解决（或者不在原始代码中），那么在某些情况下仍然存在一个可能导致问题的问题。问题是Cell.setNextState方法不能处理所有情况。具体来说，它不会设置nextState如果一个细胞是活的，并且应该是活的（它有两个或三个活的邻居）。在你的if和elif语句链上缺少else应该对我来说是个危险信号，但我在第一次检查函数时忽略了它。

以下是修复方法：

def setNextState (self , Neighbours):
    if self.state == Cell.Live and (Neighbours < 2 or Neighbours > 3):
        self.nextState = Cell.Dead
    elif self.state == Cell.Dead and Neighbours == 3:
        self.nextState = Cell.Live
    else: # remove the conditions on this block, all the state changes were handled above
        self.nextState = self.state