Plotting graph on pys60 (See related posts)

Here's the first step towards porting matplotlib to pys60.
I try to replicate some easy examples in
matplotlib tutorial.

First, we need a float range function.

from __future__ import generators

def arange(start, stop=None, step=None):
    if stop is None:
        stop = float(start)
        start = 0.0
    if step is None:
        step = 1.0
    cur = float(start)
    while cur < stop:
        yield cur
        cur += step

Then, a function to draw the axes and ticks.
In the future, this should be called automatically from plot().

from appuifw import *
app.body = canvas = Canvas()
width, height = canvas.size

def axes(xyrange, position=[18, height-11, width-10, 10], formatter=lambda x:x):
    global left, bottom, right, top, min_x, min_y, scale_x, scale_y
    left, bottom, right, top = position
    min_x, max_x, step_x, min_y, max_y, step_y = xyrange
    scale_x = float(right-left)/(max_x-min_x)
    scale_y = float(bottom-top)/(max_y-min_y)
    canvas.clear()
    canvas.rectangle([(left,top), (right+1, bottom+1)], 0)
    for x in arange(min_x, max_x, step_x):
        canvas.text((14+scale_x*(x-min_x), height-1), unicode(formatter(x)))
        canvas.point((left+scale_x*(x-min_x), bottom-1), 0)
        canvas.point((left+scale_x*(x-min_x), top+1), 0)
    for y in arange(min_y, max_y, step_y):
        canvas.text((2, bottom+2-scale_y*(y-min_y)), unicode(formatter(y)))
        canvas.point((left+1, bottom-scale_y*(y-min_y)), 0)
        canvas.point((right-1, bottom-scale_y*(y-min_y)), 0)

And lastly, the plot function. Now it has only a few features.
More will be added depending on what is needed.

def plot(xs, ys=None):
    if ys==None:
        ys = xs
        xs = range(len(ys))
    last = left+(xs[0]-min_x)*scale_x, bottom-(ys[0]-min_y)*scale_y
    for i in range(1, len(ys)):
        p = left+(xs[i]-min_x)*scale_x, bottom-(ys[i]-min_y)*scale_y
        canvas.line([last, p], 0x00000ff)
        last = p
    canvas.point(last, 0x0000ff)

When we want to plot a graph, we called both axes() and plot()

# a straight line
>>> axes([0,3.1,.5, 1,4.1,.5])
>>> plot([1,2,3,4])

# a parabola y = x^2
>>> axes([1,4.1,1, 0,16.1,2], formatter=int)
>>> plot([1,2,3,4], [1,4,9,16])

See the sreenshot of the first.