# Archived:How to plot a graph using PySymbian

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## Contents |

## Overview

There's no easy way like matplotlib for plotting simple graphs in Python. So we need to manually create functions which draw graphs. Following code shows one of the possible ways.

## Code

### Graph functions

from __future__ import generators

from appuifw import *

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

# define application body

app.body = canvas = Canvas()

width, height = canvas.size # get canvas size to scale graphs

# draw x and y axis

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()

# draw axis rectangle(see images below)

canvas.rectangle([(left,top), (right+1, bottom+1)], 0)

# define points on axis and write numbers

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)

# plot co-ordinates and generate graph

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)

### Example Usage

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])

## Postconditions

Following screenshots show the result of above code.

21 Sep

2009