sleep() function not functioning the right way in a loop (in tkinter project)

Question

in the main loop i call the sleep() function but when i execute my code, it just wait 300 times 0.01 seconds and it then displays the last frame for i=299.

from tkinter import *
from time import * 
#Those are functions a friend gave me in order to darw stuff pixel by pixel
tk=Tk()
tk.attributes('-fullscreen',True)
canvas=Canvas(tk, width=1366, height=768, background='#fff')
canvas.pack()
colors=[[(255, 255, 255) for i in range(223)] for i in range(321)]
def color(a,b,c):
    if a<10:
        va='0'+str(a)
    else:
        va=hex(a%256).replace('0x','')
    if b<10:
        vb='0'+str(b)
    else:
        vb=hex(b%256).replace('0x','')
    if c<10:
        vc='0'+str(c)
    else:
        vc=hex(c%256).replace('0x','')
    return '#%s'%(va+vb+vc)

def colr(lis):
    a=lis[0]
    b=lis[1]
    c=lis[2]
    if a%256<10:
        va='0'+str(a%256)
    else:
        va=hex(a%256).replace('0x','')
    if b%256<10:
        vb='0'+str(b%256)
    else:
        vb=hex(b%256).replace('0x','')
    if c%256<10:
        vc='0'+str(c%256)
    else:
        vc=hex(c%256).replace('0x','')
    return '#%s'%(va+vb+vc)

def fill_rect(a,b,c,d,e):
    a=a+683
    b=-b+384
    if type(e)==str:
        canvas.create_rectangle(a+2,b+2,c+a+2,d+b+2,fill=e,outline='')
    else:
        canvas.create_rectangle(a+2,b+2,c+a+2,d+b+2,fill=colr(e),outline='')
    #modifie la valeur de la couleur au pixel x,y
    for x in range(c):
        for y in range(d):
            if (a+x)>=0 and (a+x)<=320 and (b+y)>=0 and (b+y)<=222:
                colors[a+x][b+y]=e

def set_pixel(a,b,e):
    fill_rect(a,b,1,1,e)

def get_pixel(x,y):
    if x>=0 and x<=320 and y>=0 and y<=222:
        return colors[x][y]
    else:
        return (0,0,0)

#This is where my code starts
def draw_line(xa,ya,xb,yb):
    canvas.create_line(round(xa)+683,-round(ya)+384,round(xb)+683,-round(yb)+384, fill="black", width=1)
#The increment are just so the landmark is at the center of the screen

focal_length=100
def dproj(xa,ya,za,xb,yb,zb):
    draw_line(focal_length*xa/za,focal_length*ya/za,focal_length*xb/zb,focal_length*yb/zb)

#Vertex table of the cube
a=[-1,-1,1]
b=[1,-1,1]
c=[1,1,1]
d=[-1,1,1]
e=[-1,-1,3]
f=[1,-1,3]
g=[1,1,3]
h=[-1,1,3]
for i in range(300):
    canvas.delete("all")
    focal_length=i
#Edges table
    dproj(a[0],a[1],a[2],b[0],b[1],b[2])
    dproj(a[0],a[1],a[2],d[0],d[1],d[2])
    dproj(a[0],a[1],a[2],e[0],e[1],e[2])
    dproj(c[0],c[1],c[2],b[0],b[1],b[2])
    dproj(c[0],c[1],c[2],d[0],d[1],d[2])
    dproj(c[0],c[1],c[2],g[0],g[1],g[2])
    dproj(f[0],f[1],f[2],b[0],b[1],b[2])
    dproj(f[0],f[1],f[2],e[0],e[1],e[2])
    dproj(f[0],f[1],f[2],g[0],g[1],g[2])
    dproj(h[0],h[1],h[2],d[0],d[1],d[2])
    dproj(h[0],h[1],h[2],e[0],e[1],e[2])
    dproj(h[0],h[1],h[2],g[0],g[1],g[2])
    sleep(0.01)

i wanted to make some kind of 3D render of a cube with the focal lenght slowly changing to make kind of a zoom in effect. I also tried sys.stdout.flush() but same issue although maybe this only applies for prints in terminal.