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Mark Ivey’s weblog

Graphy A Chart Library for Python

In my 20% time at work, I’ve been writing a Python library for generating charts using Google’s Chart API. It is called graphy, and is now available as open source software on code.google.com.

I’ve frequently wanted to visualize data for various projects I’m working on but have been frustrated because the tools I’ve used are too heavyweight for making simple charts. When the opportunity came up to use the Google Chart API, I jumped at the chance to make a chart library I would enjoy using. The basic philosophy of graphy is to let you present your data naturally and then get out of your way.

I’ll give a couple examples of how it is used. If you’re interested, there are more examples in the user guide and in the source code. First, a simple bar chart showing how population has changed over the past 4 decades in three bay area cities:

from graphy.backends import google_chart_api

cities = ('San Jose', 'San Francisco', 'Oakland')
pop_1960 = (200000, 740000, 370000)
pop_2000 = (900000, 780000, 400000)

chart = google_chart_api.BarChart()
chart.AddBars(pop_1960, label='1960', color='ccccff')
chart.AddBars(pop_2000, label='2000', color='0000aa')
chart.vertical = False
chart.left.labels = cities
chart.bottom.min = 0
print chart.display.Img(300, 180)

That snippet gives this chart:

Next an example using a line chart to compare average temperature trends in two US cities:

from graphy.backends import google_chart_api
from graphy import formatters
from graphy import line_chart

# Average monthly temperature
sunnyvale = \
    [49, 52, 55, 58, 62, 66, 68, 68, 66, 61, 54, 48, 49]
chicago = \
    [25, 31, 39, 50, 60, 70, 75, 74, 66, 55, 42, 30, 25]

chart = google_chart_api.LineChart()
chart.AddLine(sunnyvale, label='Sunnyvale')
chart.AddLine(chicago, label='Chicago',
chart.bottom.labels = ['Jan', 'Apr', 'Jul', 'Sep', 'Jan']

chart.left.min = 0
chart.left.max = 80
chart.left.labels = [10, 32, 50, 70]
chart.left.label_positions = [10, 32, 50, 70]
print chart.display.Img(350, 170)

Here’s the resulting chart:

Check out the graphy project page for more information, including the full user guide and source code for graphy 1.0, released under the Apache 2 license.