如何解决python2.7中的名称错误

Question

当我在python3中运行Python脚本时，它运行得很好，但是在Python 2.7中我遇到了一个错误，我应该在Python 2.7中运行以下代码：

这是我的代码：我想要要测试一些路径查找算法，并希望创建一个由网格组成的窗口，在其中我可以在单击时拖动鼠标来创建墙，并通过右键单击和拖动来删除它们

import Tkinter

class Cell():
    FILLED_COLOR_BG = "green"
    EMPTY_COLOR_BG = "white"
    FILLED_COLOR_BORDER = "green"
    EMPTY_COLOR_BORDER = "black"

    def __init__(self, master, x, y, size):
        """ Constructor of the object called by Cell(...) """
        self.master = master
        self.abs = x
        self.ord = y
        self.size= size
        self.fill= False

    def _switch(self):
        """ Switch if the cell is filled or not. """
        self.fill= not self.fill

    def draw(self):
        """ order to the cell to draw its representation on the canvas """
        if self.master != None :
            fill = Cell.FILLED_COLOR_BG
            outline = Cell.FILLED_COLOR_BORDER

            if not self.fill:
                fill = Cell.EMPTY_COLOR_BG
                outline = Cell.EMPTY_COLOR_BORDER

            xmin = self.abs * self.size
            xmax = xmin + self.size
            ymin = self.ord * self.size
            ymax = ymin + self.size

            self.master.create_rectangle(xmin, ymin, xmax, ymax, fill = fill, outline = outline)

class CellGrid(Canvas):
    def __init__(self,master, rowNumber, columnNumber, cellSize, *args, **kwargs):
        Canvas.__init__(self, master, width = cellSize * columnNumber , height = cellSize * rowNumber, *args, **kwargs)

        self.cellSize = cellSize

        self.grid = []
        for row in range(rowNumber):

            line = []
            for column in range(columnNumber):
                line.append(Cell(self, column, row, cellSize))

            self.grid.append(line)

        #memorize the cells that have been modified to avoid many switching of state during mouse motion.
        self.switched = []

        #bind click action
        self.bind("<Button-1>", self.handleMouseClick)  
        #bind moving while clicking
        self.bind("<B1-Motion>", self.handleMouseMotion)
        #bind release button action - clear the memory of midified cells.
        self.bind("<ButtonRelease-1>", lambda event: self.switched.clear())

        self.draw()



    def draw(self):
        for row in self.grid:
            for cell in row:
                cell.draw()

    def _eventCoords(self, event):
        row = int(event.y / self.cellSize)
        column = int(event.x / self.cellSize)
        return row, column

    def handleMouseClick(self, event):
        row, column = self._eventCoords(event)
        cell = self.grid[row][column]
        cell._switch()
        cell.draw()
        #add the cell to the list of cell switched during the click
        self.switched.append(cell)

    def handleMouseMotion(self, event):
        row, column = self._eventCoords(event)
        cell = self.grid[row][column]

        if cell not in self.switched:
            cell._switch()
            cell.draw()
            self.switched.append(cell)


if __name__ == "__main__" :
    app = Tk()

    grid = CellGrid(app, 50, 50, 10)
    grid.pack()

    app.mainloop()

和错误：

NameError: name 'Canvas' is not defined

如何更改代码以便在Python2.7中运行它？你知道吗

Answer 1

好吧，它没有定义好，我想知道它怎么能在Py3上运行，除非Tkinter以某种方式将Canvas转储到您的命名空间中。你知道吗

你可能想做class CellGrid(Tkinter.Canvas)，但我不记得Tkinter的确切结构，所以它可能是在一个子包或什么的。你知道吗

Answer 2

在您的情况下，需要导入要使用的模块元素：

from Tkinter import Canvas, Tk

您还可以执行以下操作：

from Tkinter import * 

但这不是推荐的做法。如果您使用了许多模块，并且其中两个恰好具有相同的方法名，那么您的代码可能无法正常工作。你知道吗

最后一条路就是

import Tkinker

但是每次使用这个模块的元素时，都需要添加完整路径，所以如果要使用Canvas，就需要使用Tkinker.Canvas。你知道吗

还要记住，在Python2.7中，import Tkinter和在3.X中import tkinter