Timeline Graph

#!/usr/bin/env python
"""
Script to generate a yearly-timeline google Chart API graph,
using pygooglechart for the graph and PIL to join the graphs together.
2010/09/05 22:04:45
Matt Behrens <askedrelic@gmail.com> 

Assuming date data in some format like this:
2003-04
2003-08
2004-02
2003-07
"""

import calendar
import glob, os

import pygooglechart
import Image

def graphThreeYears(orig_start_year):
    total_years = 3

    #start empty
    months = []
    years = []

    #setup graph
    chart = pygooglechart.GroupedVerticalBarChart(825, 250, y_range=(0, 20))
    chart.set_bar_width(14)
    chart.set_grid(0, 10, 5, 5)

    #build empty arrays of month/year combo
    start_year = orig_start_year
    for y in xrange(total_years):
        #build the monthly abbrevations
        months += [x for x in calendar.month_abbr if x]
        #build the empty year array
        years += [''] * 12
        #then fill in January position
        years[y * 12] = ' %s' % start_year
        start_year += 1

    #fill in the dates
    dates = []
    start_year = orig_start_year
    for y in xrange(total_years):
        for m in xrange(1,13):
            count = 0
            dates.append(count)
        start_year += 1

    chart.add_data(dates)

    #setup the double label axes
    chart.set_axis_labels('x', months)
    chart.set_axis_labels('x', years)
    #y labels every 2 points, except for the starting point, which is going to be empty
    chart.set_axis_labels('y', [''] + [x for x in range(21) if x % 2 == 0 and x != 0 ])

    chart.download('%s-%s.png' % (orig_start_year, orig_start_year+total_years))

#actually create the graphs
start_year = 2002
end_year = 2002+3*5
for year in xrange(start_year,end_year, 3):
    graphThreeYears(year)

#new large canvas to work with
nim = Image.new("RGB", (5000,300), "white")
#most of the cropping and specific pixel values come from trial/error tweaking
x = 809
counter = 0
for file in glob.iglob('20*-*.png'):
    #if the first graph, start at 0
    if counter == 0:
        im = Image.open(file)
        nim.paste(im, (0,40))
    #otherwise, crop the y labels from future graphs
    else:
        im = Image.open(file)
        im = im.crop((18,0,825,250))
        nim.paste(im, (x,40))
        x += 790
    counter += 1

nim.save('graph.png')