def snpplot(args):
    """
    %prog counts.cdt

    Illustrate the histogram per SNP site.
    """
    p = OptionParser(snpplot.__doc__)
    opts, args, iopts = p.set_image_options(args, format="png")

    if len(args) != 1:
        sys.exit(not p.print_help())

    datafile, = args
    # Read in CDT file
    fp = open(datafile)
    next(fp)
    next(fp)
    data = []
    for row in fp:
        atoms = row.split()[4:]
        nval = len(atoms)
        values = [float(x) for x in atoms]
        # normalize
        values = [x * 1. / sum(values) for x in values]
        data.append(values)

    pf = datafile.rsplit(".", 1)[0]
    fig = plt.figure(1, (iopts.w, iopts.h))
    root = fig.add_axes([0, 0, 1, 1])
    xmin, xmax = .1, .9
    ymin, ymax = .1, .9
    yinterval = (ymax - ymin) / len(data)
    colors = "rbg" if nval == 3 else ["lightgray"] + list("rbg")
    ystart = ymax
    for d in data:
        xstart = xmin
        for dd, c in zip(d, colors):
            xend = xstart + (xmax - xmin) * dd
            root.plot((xstart, xend), (ystart, ystart), "-", color=c)
            xstart = xend
        ystart -= yinterval

    root.text(.05, .5, "{0} LMD50 SNPs".format(len(data)),
              ha="center", va="center", rotation=90, color="lightslategray")

    for x, t, c in zip((.3, .5, .7), ("REF", "ALT", "HET"), "rbg"):
        root.text(x, .95, t, color=c, ha="center", va="center")
    normalize_axes(root)

    image_name = pf + "." + iopts.format
    savefig(image_name, dpi=iopts.dpi, iopts=iopts)
%prog counts.cdt

    Illustrate the histogram per SNP site.