why my Tiled collisions doesn´t work in my pygame project?

Im following a tutorial to make a game working with some pygame tiled and pytmx stuff, but however, we added a new object´s layer with some empty rectangles over the tiles where the player is not being able to enter, then we maked a wall´s list to put inside this "walls" and then we maded a couple of functions to check if the player is over the collision obstacle, and if that´s the case move the player one step back, but when I run the game, it opens the map and I can actually move my player around, but when I test the obstacle surface and collisions, it´s not working, and the player can go over the "walls". could you please help me to solve this, here I leave my wall´s code (inside of my Game Class):

def update(self): self.group.update() #verification du collision for sprite in self.group.sprites(): if sprite.feet.collidelist(self.walls) > - 1: sprite.move_back() def run(self): clock = pygame.time.Clock() #boucle du jeu running = True while running: self.player.save_location() self.handle_input() self.update() self.group.center(self.player.rect) self.group.draw(self.screen) pygame.display.flip() for event in pygame.event.get(): if event.type == pygame.QUIT: running = False clock.tick(60) pygame.quit() 

But... on the tutorial in Tiled software on the Obstacle information, there´s an option to put the "type" of object, at least that says on the tutorial, but in my Tiled, says "Class" instead of " Type" I think is the same, but however, I tried to put Class instead of Type in collision code, but... you know that Class is a reserved word by python, so... I put back " Type", I´m not sure if this sort of information matters, but maybe yes, in my tmx_map, on the obstacles layer I already set the "class" ("type object") of each object as "Collision" anyway, here´s the Player´s code

class Player(pygame.sprite.Sprite): def __init__(self, x, y): super().__init__() self.sprite_sheet = pygame.image.load('player.png') self.image = self.get_image(0,0) self.image.set_colorkey([0,0,0]) self.rect = self.image.get_rect() self.position = [x,y] self.images = { 'down':self.get_image(0,0), 'left' :self.get_image(0,32), 'right':self.get_image(0,64), 'up' :self.get_image(0,96), } self.feet = pygame.Rect(0,0, self.rect.width * 0.5, 12) self.old_position = self.position.copy() self.speed = 2 def save_location(self): self.old_position = self.position.copy() def update(self): self.rect.topleft = self.position self.feet.midbottom = self.rect.midbottom def move_back(self): self.position = self.old_position self.rect.topleft = self.position self.feet.midbottom = self.rect.midbottom 

thanks in advance