I have this project to build a perfect maze recursively by using python. I have a MyStack class which creates a stack to track the path that I go through. And a Cell class which represent each square within the maze and store some information. I think I complete the code but IDLE gives me some error that I couldn't figure out. Here is the code.

from random import *
from graphics import *class MyStack:def __init__(self):self.S = []def push(self, item):self.S.insert(0, item)def pop(self):return self.S.pop(0)def isEmpty(self):return True if len(self.S) == 0 else Falsedef size(self):return len(self.S)class Maze:def __init__(self, N):self.size = Nself.maze = [[i for i in range(N + 2)] for i in range(N + 2)]for r in range(self.size + 2):for c in range(self.size + 2):self.maze[r][c] = Cell()def walk(self, s, x, y):neighboor = [(x + 1, y), (x - 1, y), (x, y + 1), (x, y - 1)]if s.size() == self.size**2: returnelse:new = choice(neighboor)while self.maze[new[0]][new[1]].getVisit():while new[0] < 1 or new[1] > self.size:new = choice(neighboor)if neighboor != []: new = choice(neighboor.remove(new))else:temp = s.pop(s)x, y = temp[0], temp[1]self.walk(s, x, y)if new == neighboor[0]:self.maze[x][y].changeNorth()self.maze[new[0]][new[1]].changeSouth()elif new == neighboor[1]:self.maze[x][y].changeSouth()self.maze[new[0]][new[1]].changeNorth()elif new == neighboor[2]:self.maze[x][y].changeEast()self.maze[new[0]][new[1]].changeWest()elif new == neighboor[3]:self.maze[x][y].changeWest()self.maze[new[0]][new[1]].changeEast()s.push(new)self.walk(s, new[0], new[1])def search(self):startX, startY = randint(1, self.size), randint(1, self.size)s = MyStack()temp = (startX, startY)s.push(temp)self.maze[startX][startY].changeVisit()self.walk(s, startX, startY)def draw(self):win = GraphWin()startXY = Point(27, 27)start = Circle(startXY, 5)start.setOutline('orange')start.setFill('orange')start.draw(win)x, y = 20, 20for r in range(1, self.size + 1):for c in range(1, self.size + 1):if self.maze[r][c].getNorth():unit = Line(Point(x, y), Point(x + 15, y))unit.draw(win)x, y = x + 15, yx, y = 20, y + 15x, y = 20, 20for c in range(1, self.size + 1):for r in range(1, self.size + 1):if self.maze[r][c].getWest():#print(self.maze[r][c].getWest())unit = Line(Point(x, y), Point(x, y + 15))unit.draw(win)x, y = x, y + 15x, y = x + 15, 20x, y = 20, self.size * 15 + 20for c in range(1, self.size + 1):if self.maze[self.size][c].getSouth():unit = Line(Point(x, y), Point(x + 15, y))unit.draw(win)x, y = x + 15, yx, y = self.size * 15 + 20, 20for r in range(1, self.size + 1):if self.maze[self.size][c].getEast():unit = Line(Point(x, y), Point(x, y + 15))unit.draw(win)x, y = x, y + 15class Cell:def __init__(self):#self.x = x#self.y = yself.north = Trueself.south = Trueself.east = Trueself.west = Trueself.visit = Falsedef changeVisit(self):self.visit = Truedef changeNorth(self):self.north = Falsedef changeSouth(self):self.south = Falsedef changeEast(self):self.east = Falsedef changeWest(self):self.west = Falsedef getVisit(self):return self.visitdef getNorth(self):return self.northdef getSouth(self):return self.southdef getEast(self):return self.eastdef getWest(self):return self.west

Here is the Error I got:

>>> a = Maze(5)
>>> a.search()
Traceback (most recent call last):File "<pyshell#1>", line 1, in <module>a.search()File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 91, in searchself.walk(s, startX, startY)File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 48, in walkwhile self.maze[new[0]][new[1]].getVisit():
IndexError: list index out of range

I'm new to programming, any help would be appreciate. Thank you~

After fix the previous one, I got an error for the line

    if len(neighboor) != 0: new = choice(neighboor.remove(new))

The error message is

Traceback (most recent call last):File "<pyshell#11>", line 1, in <module>a.search()File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 88, in searchself.walk(s, startX, startY)File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 73, in walkself.walk(s, new[0], new[1])File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 52, in walkif len(neighboor) != 0: new = choice(neighboor.remove(new))File "C:\Python34\lib\random.py", line 253, in choicei = self._randbelow(len(seq))
TypeError: object of type 'NoneType' has no len()

But I define 'neighboor' as a list, it should has a len()

Thank you so much for help! plzplz~

The problem is that you're not ensuring that the steps in your walk are valid.

The way you have it currently, walk could pick a neighboor that is out of the bounds of the maze. For example, if a maze is 5x5, attempting to access maze[5][?] or maze[?][5] will result in an IndexError like you get.

To fix this, you could define an is_valid method for your maze class, e.g.:

def is_valid(self, x, y):return (0 <= x < self.size) and (0 <= y < self.size)

Then, you when you pick a neighboor, you ensure it's valid:

#...
else:new = choice(neighboor)while self.is_valid(new[0], new[1]) == False:new = choice(neighboor)while self.maze[new[0]][new[1]].getVisit():
#...

This snippet picks a neighboor, then, if it's not valid, regenerates new until it finds a valid one.

But this loop would be better written as:

#...
else:while True:new = choice(neighboor)if self.is_valid(new[0], new[1]): breakwhile self.maze[new[0]][new[1]].getVisit():
#...

There are more problems with your code, however, as you'll eventually see, but this will get you past this specific one.