This was translated from a cool script posted on Perl Monks. Took me an indecent amount of time.
First we choose a few fixed points on the screen, call them v1, v2... A Voronoi neighbourhood of 'vn' is the set of points that closer to it than to any other v. The script below shades the points by seeing if they're on the boundary between two V-neighbourhoods, really close to a fixed one or somewhere in the middle.
#!/usr/bin/python from math import * import random chars = ". , - + * $ & # @ ~ ~ ".split() (rows,cols) = (40,80) points = 8 xfact = 1.0/rows yfact = 1.0/cols xs =  ys =  #generate a few random points v1...vn for i in range(0,points): (xrand,yrand) = (random.random(),random.random()) print "%f %f"%(xrand,yrand) for xoff in range(-1,2): for yoff in range(-1,2): xs.append(xrand+xoff) ys.append(yrand+yoff) #function to find the closest of the vi def closest(x,y,xs,ys): (best,good) = (99.0,99.0) for i in range(0,len(xs)): dist = sqrt((x-xs[i])**2.0+(y-ys[i])**2.0) if (dist < best): (best,good) = (dist,best) elif dist < good: good = dist return (best,good) screen =  for i in range(0,rows): screen.append(" ") #generate screen for i in range(0,rows): x = i*xfact; for j in range(0,cols): y = j*yfact; (best,good) = closest(x,y,xs,ys) screen[i] = screen[i] + chars[int(10*best/good)] for i in range(0,rows): print screen[i]