# Tk_avoidance_walk_4.py

# Tk_avoidance_walk_4.py

import random
from Tkinter import *
from math import *

ri = random.randint
rs = random.shuffle
rc = random.choice

ww = 600
hh = 600

root = Tk()
root.title("Tk_avoidance_walk")
root.geometry("%dx%d+-6+-2"%(ww,hh))
cv = Canvas(width=ww, height=hh, bg='white')
cv.pack()

steps = ["N","E","S","W"]
tries = 0
def direction():
    if not tries:
        t = steps[:]
        rs(t)
        return [t]
    return [rc([steps[:], steps[::-1]])]

r = 10
grid = dict([((x,y), 0) for x in range(r,ww-r) for y in range(r,hh-r)])
x,y = ww/2, hh/2
xy = [(x,y)]
zz = []

most = 0

while 1:
    while 1:
        try:
            x,y = xy[-1]
            step = zz[-1].pop()
            break
        except:
            try:
                xy.pop()
                zz.pop()
            except:
                xy = [(x,y)]
                zz += direction()
    if   step == "E":
        x += r
    elif step == "W":
        x -= r
    elif step == "N":
        y += r
    else:
        y -= r
    try:
        grid[x,y]
        if (x,y) not in xy:
            zz += direction()
            xy += [(x,y)]
            if len(xy) > most:
                most = len(xy)
                print most
            tries = max(0,tries-3)
            cv.delete('all')
            cv.create_line(xy,fill='blue')
            cv.update()
        else:
            tries += 1
            if tries > 12:
                xy = xy[:-50]
                zz = zz[:-50]
    except:
        0