Python Pygame 2D weird array

Question

I made a program in Pygame where you walk in a maze. The maze is a 2D array which contains either
True: the wall is there or
False: the wall is not there
It works fine. But when I go to position 8;9 I can now go right - through a wall. It happens only on this y position. When I check the right variable, it is False.

import pygame
from pygame.locals import *
from pygame import gfxdraw
white = (255, 255, 255)
width, height = 220, 220
screen = pygame.display.set_mode((width, height))
psurf = pygame.Surface((20, 20))
psurf.fill((0, 0, 0))
wallsurf = pygame.Surface((20, 20))
wallsurf.fill((255, 0, 0))

t = True
f = False

walls = [[f, t, f, f, f, f, f, f, f, f, f],
         [f, t, f, f, f, f, f, f, f, f, f],
         [f, t, f, f, t, t, t, t, t, f, f],
         [f, t, f, f, t, f, f, f, t, f, f],
         [f, t, f, f, t, f, f, f, t, f, f],
         [f, t, f, f, t, f, f, f, t, f, t],
         [f, t, f, f, t, f, f, f, t, f, t],
         [f, t, f, f, t, f, f, f, t, f, t],
         [f, t, f, f, t, f, f, f, f, f, t],
         [f, t, t, f, t, t, t, t, t, t, t],
         [f, f, f, f, f, f, f, f, f, t, t]]

px = 0
py = 0
move_ticker = 0
right = True
left = True
delay = 500
maze = pygame.Surface((220, 220))
maze.fill(white)
placex = 0
placey = 0
for row in walls:
        placex = 0
        for wall in row:
            if wall == True:
               maze.blit(wallsurf, (placex * 20, placey * 20))
            placex += 1
        placey += 1
while True:
    pygame.event.get()
    screen.fill(white)
    screen.blit(maze, (0, 0))
    screen.blit(psurf, (px, py))
    keys=pygame.key.get_pressed()
    if keys[K_LEFT]:
        if left:
           if move_ticker == 0:
               move_ticker = delay
               px -= 20
               if px < -1:
                   px = 0
    if keys[K_RIGHT]:
        if right:
           if move_ticker == 0:   
               move_ticker = delay
               px += 20
               if px > 200:
                   px = 200
    if keys[K_DOWN]:
        if down:
            if move_ticker == 0:   
                move_ticker = delay   
                py += 20
                if py >= 200:
                    py = 200
    if keys[K_UP]:
        if up:
            if move_ticker == 0:   
                move_ticker = delay 
                py -= 20
                if py < 0:
                    py = 0
    if move_ticker > 0:
       move_ticker -= 1
    truex = int(px / 20)
    truey = int(py / 20)
    right = True
    left = True
    up = True
    down = True
    try:
        if walls[truey-1][truex]:
            up = False
        if walls[truey+1][truex]:
            down = False
        if walls[truey][truex-1]:
            left = False
        if walls[truey][truex+1]:
            right = False
    except IndexError:
        pass       
    pygame.display.flip()

Nathan · Accepted Answer · 2018-04-04 19:53:07Z

The issue is that you have one try statement instead of 4. When you get to the lowest row walls[truey+1][truex] will return an index error. Right is still set to True and is therefor never updated to False. A quick (and ugly) fix is:

try:
    if walls[truey-1][truex]:
        up = False
except IndexError:
        up = False
try:
    if walls[truey+1][truex]:
        down = False
except IndexError:
        down = False
try:
    if walls[truey][truex-1]:
        left = False
except IndexError:
        left = False    
try:
    if walls[truey][truex+1]:
        right = False
except IndexError:
        right = False

I think a prettier way is to use a function, a function is a piece of code you can re-use multiple times so you don't have to rewrite the same thing over and over.

def can_move(pos_x, pos_y, dx, dy, walls):
    move = True
    try:
        if walls[pos_y + dy][pos_x + dx]:
            move = False
    except IndexError:
        move = False
    return move

Which you can shorten to:

def can_move(pos_x, pos_y, dx, dy, walls):
    try:
        move = not(walls[pos_y + dy][pos_x + dx])
    except IndexError:
        move = False
    return move

Using this function you can define your movements:

right = can_move(truex, truey, 1, 0, walls)
left = can_move(truex, truey, -1, 0, walls)
up = can_move(truex, truey, 0, -1, walls)
down = can_move(truex, truey, 0, 1, walls)

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