moving letters

from random import randint
from copy import deepcopy
grid=[[' ' for _ in range(10)] for _ in range(10)]
letters='qwertyuiopasdfghjklzxcvbnm'
posx,posy=0,0
done=1
def displaygrid():
    for row in grid:
        print('\n+--+--+--+--+--+--+--+--+--+--+\n|',end='')
        for col in row:
            print(col,end=' |')
    print('\n+--+--+--+--+--+--+--+--+--+--+')
while done:
    displaygrid()
    grid[posy][posx]=letters[randint(0,25)]
    randlist=[]
    if posy!=0 and grid[posy-1][posx]==' ':
        randlist+=[0]
    if posx!=9 and grid[posy][posx+1]==' ':
        randlist+=[1]
    if posy!=9 and grid[posy+1][posx]==' ':
        randlist+=[2]
    if posx!=0 and grid[posy][posx-1]==' ':
        randlist+=[3]
    if not randlist:
        done=0
    else:
        direction=randlist[randint(0,len(randlist)-1)]
        if direction==0:
            posy-=1
        elif direction==1:
            posx+=1
        elif direction==2:
            posy+=1
        else:
            posx-=1
displaygrid()