Stacked bar graph.

hi, I'm having trouble figuring out how to add a few more

    > layers to a stacked bar graph. What I have so far is:

    > p1 =, data['n'], width, color='r') p2
    > =, data['l'], width, color='y',
    > bottom=data['n']) p3 =, data['m'], width,
    > color='b', bottom=data['l']) p4 =, data['h'],
    > width, color='g', bottom=data['m'])

    > But I don't think this is correct. I only get two layers
    > (red and green). Does anyone know the proper method?

See examples/ -- you need to keep a cumulative sum of the
bottom positions, eg

yoff = array([0.0] * len(colLabels)) # the bottom values for stacked bar chart
for row in xrange(rows):
    bar(ind, data[row], width, bottom=yoff, color=colours[row])
    yoff = yoff + data[row]
    cellText.append(['%1.1f' % (x/1000.0) for x in yoff])