Walls that block the movement of a player

wall_of_blocks_with_player.py

import pygame
pygame.init()
screen = pygame.display.set_mode((400, 300))
done = False
clock = pygame.time.Clock()
x,y = 170,120
walls=[]
for horiz in range(0,400,25): walls.append(pygame.Rect(horiz,0,25,25)) #top wall
for horiz in range(0,400,25): walls.append(pygame.Rect(horiz,275,25,25)) #bottom wall
for vert in range(0,325,25): walls.append(pygame.Rect(0,vert,25,25)) #left wall
for vert in range(0,325,25): walls.append(pygame.Rect(375,vert,25,25)) #right wall
while not done:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            done = True
    pressed = pygame.key.get_pressed()
    xprevious = x
    yprevious = y
    if pressed[pygame.K_UP]: y = y - 3
    if pressed[pygame.K_DOWN]: y = y + 3
    if pressed[pygame.K_LEFT]: x = x - 3
    if pressed[pygame.K_RIGHT]: x = x + 3
    me = pygame.Rect(x, y, 60, 60)
    if me.collidelistall(walls) != []: #no collisions returns an empty list
        x = xprevious
        y = yprevious
        me = pygame.Rect(x, y, 60, 60)
    screen.fill((255, 255, 255))
    pygame.draw.rect(screen, (0,0,0), me)
    for wall in walls:
        pygame.draw.rect(screen, (255,0,0), wall)
    pygame.display.flip()
    clock.tick(60)
pygame.quit()