Python mandelbrot set generator

mandelbrot.py

#!/usr/bin/env python

import argparse
import sys
import os

trace = False

def pixel_n(x0, y0, escape):
    x=0.
    y=0.
    for i in xrange(escape):
        x2 = x*x
        y2 = y*y
        if x2 + y2 > 2*2:
            return (True, i)
        x, y = x2 - y2 + x0, 2*x*y + y0
        if trace: print (x0, y0, i, x, y)
    return (False, escape)

def pixel(x0, y0, escape, xmin, xmax, ymin, ymax):
    clamp = lambda val, low, high: val * (high - low) + low
    return pixel_n(clamp(x0, xmin, xmax), clamp(y0, ymin, ymax), escape)

def mandel(w, h, escape, xmin=-2.5, xmax=1., ymin=-1., ymax=1.):
    return [[pixel(float(x)/w, float(y)/h, escape, xmin, xmax, ymin, ymax)
             for x in xrange(w)] for y in xrange(h)]

def pixel_s(px):
    escapes, at = px
    if escapes:
        return "%3d" % at
    return "   "

def mandel_s(m):
    return '\n'.join(' '.join(pixel_s(px) for px in line) for line in m)

def main():
    ap = argparse.ArgumentParser(description="Mandelbrot set generator")
    ap.add_argument('--width', type=int)
    ap.add_argument('--height', type=int)
    ap.add_argument('--xmin', type=float, default=-2.5)
    ap.add_argument('--xmax', type=float, default=1.)
    ap.add_argument('--ymin', type=float, default=-1.)
    ap.add_argument('--ymax', type=float, default=1.)
    ap.add_argument('--escape', type=int, default=99)
    ap.add_argument('--trace', action='store_true')
    a = ap.parse_args()

    trace = a.trace

    th, tw = os.popen('stty size', 'r').read().split()
    w = a.width or (int(tw) or 80)/4
    h = a.height or (int(th) or 24)-1

    if trace: print (h, w, a.escape, a.xmin, a.xmax, a.ymin, a.ymax)

    print mandel_s(mandel(w=w, h=h, escape=a.escape,
        xmin=a.xmin, xmax=a.xmax, ymin=a.ymin, ymax=a.ymax))

if __name__ == "__main__":
    main()