build a perfect maze recursively in python

Question

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 False

    def size(self):
        return len(self.S)

class Maze:
    def __init__(self, N):

        self.size = N
        self.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: return

        else:
            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, 20


        for 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, y

            x, y = 20, y + 15

        x, y = 20, 20
        for 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 + 15

            x, y = x + 15, 20

        x, y = 20, self.size * 15 + 20
        for 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, y

        x, y = self.size * 15 + 20, 20
        for 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 + 15

class Cell:
    def __init__(self):
        #self.x = x
        #self.y = y
        self.north = True
        self.south = True
        self.east = True
        self.west = True
        self.visit = False

    def changeVisit(self):
        self.visit = True

    def changeNorth(self):
        self.north = False

    def changeSouth(self):
        self.south = False

    def changeEast(self):
        self.east = False

    def changeWest(self):
        self.west = False

    def getVisit(self):
        return self.visit

    def getNorth(self):
        return self.north

    def getSouth(self):
        return self.south

    def getEast(self):
        return self.east

    def 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 search
    self.walk(s, startX, startY)
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 76, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 48, in walk
    while 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 search
    self.walk(s, startX, startY)
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 73, in walk
    self.walk(s, new[0], new[1])
  File "C:\Users\Serena\Desktop\XAproject\Stack.py", line 52, in walk
    if len(neighboor) != 0: new = choice(neighboor.remove(new))
  File "C:\Python34\lib\random.py", line 253, in choice
    i = 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~

Answer 1

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]): break

    while 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.