Maze solver won't backtrack in Python - python-3.x

Question

There are a couple of maze questions similar to this one but none of them ever really go into the why it won't work.
I don't need precise answers. I just need to know why this particular thing doesn't work.
This is the bit of my class Maze that I need help with.
ysize in my example is 10
xsize is 10
xend is 20 (changing it to 19 messes with the results and doesn't draw anything)
yend is 10 (changing it to 9 does this too)
class Maze:
def __init__(self):
self.maze = []
self.xstart = None
self.ystart = None
self.xend = None
self.yend = None
self.xsize = None
self.ysize = None
def read_maze(self, filename):
maze_list = []
f_maze = open(filename)
size = f_maze.readline().split() #
start = f_maze.readline().split() #
end = f_maze.readline().split() #
self.xstart = int(start[1])
self.ystart = int(start[0])
self.xend = (int(end[1])*2)
self.yend = (int(end[0])*2)
self.xsize = (int(size[1])*2)
self.ysize = (int(size[0])*2)
lines = f_maze.readlines()
for line in lines:
maze_list.append(list(line[:len(line)]))
self.maze = maze_list # Assigns to class
def __str__(self):
return ("".join(''.join(line) for line in self.maze))
def solve(self, x, y):
if y > (self.ysize) or x > (self.xsize):
print("1")
return False
if self.maze[y][x] == self.maze[self.yend][self.xend]:
print("2")
return True
if self.maze[y][x] != " ":
print("3")
return False
self.maze[y][x] = "o" # MARKING WITH o for path already taken.
if self.solve(x+1,y) == True:
return True
elif self.solve(x,y+1) == True:
return True
elif self.solve(x-1,y) == True:
return True
elif self.solve(x,y-1) == True:
return True
self.maze[y][x] = " " # ELSE I want it to be replaced with space
return False
This is the current result.
---------------------
|ooooooooooooo| | |
|-+-+-+ +-+-+o+ + +-|
| | | |o| |
| +-+-+ + +-+-+-+ + |
| | | | | |
|-+-+ + + + +-+ +-+-|
| | |
|-+ +-+-+-+-+-+ +-+ |
| | | |
---------------------
I want it like this:
---------------------
|ooooooo | | |
|-+-+-+o+-+-+ + + +-|
| | o| | | |
| +-+-+o+ +-+-+-+ + |
| o| | | | |
|-+-+ +o+ + +-+ +-+-|
| |ooooooooooooo|
|-+ +-+-+-+-+-+ +-+o|
| | | o|
---------------------
I don't know how to fix the indentation format here I apologize. That is my whole code. These are my test statements:
maze = Maze()
maze.read_maze(filename)
maze.solve(maze.xstart, maze.ystart)
print(maze)
The files go in this format saved as .txt files.
5 10
1 1
5 10
---------------------
| | | |
|-+-+-+ +-+-+ + + +-|
| | | | | |
| +-+-+ + +-+-+-+ + |
| | | | | |
|-+-+ + + + +-+ +-+-|
| | |
|-+ +-+-+-+-+-+ +-+ |
| | | |
---------------------

Answer 1

The problem is that as your file stands, xend, yend is (10, 20). To debug why it's not working, you can print(self.maze[self.yend][self.xend]) which returns a dash "-". Now, when your recursive call's (x, y) pair reaches its first dash, it tests True for the line
if self.maze[y][x] == self.maze[self.yend][self.xend]:
and thinks it has solved the maze. Rather, we want to test
if (y, x) == (self.yend, self.xend):
That is, test the coordinates, not the value of the square.
Another point: examining the actual location of the goal, we see that it's here:
+-+ +-+ |
| |
--------- <= this corner is the goal!
Which is unreachable if moving in strictly cardinal directions. Moving the goal a square up or to the left would put it within bounds of the solver algorithm.
This was sufficient to get the code working for me and hopefully is enough to get you moving again.