Pretty Python Plotting With CairoPlot

Monday Apr 4th 2011 by Akkana Peck
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Data aficionados constantly on the lookout for better ways to display charts and graphs will appreciate CairoPlot, Python-based plotting software pretty enough to impress even the most jaded Mac user.

As a data junkie, I'm forever looking for better ways to display charts and graphs, especially from Python. There are lots of Python plotting packages available, but if you want output that's pretty enough that even your Mac friends will be impressed, consider using CairoPlot.

CairoPlot isn't packaged for most distros, but it's an easy install. The current release is version 1.1 at the CairoPlot Launchpad page. You can download the cairoplot-1.1.tar.gz from there, or check it out with bzr if you prefer. (Once 1.2 is ready the project may move to Sourceforge.)

First, extract the tarball:

$ tar xvf cairoplot-1.1.tar.gz

then, copy one file, cairoplot-1.1/CairoPlot.py, to the directory where you'll be developing your Python script.

Pie Charts: Who's Sending Spam?

When playing with plotting, finding a good source of data is always the first step. For this project, let's analyze a Postfix log file, /var/log/mail.info to look at the sources of one class of spam.

A casual glimpse through the file reveals we're getting a lot of mail delivery attempts where the sender claims an address that doesn't really exist, like this one:

Mar 5 15:05:45 mailserver postfix/smtpd[29764]: NOQUEUE: reject: RCPT from 212.199.94.45.static.012.net.il[212.199.94.45]: 450 4.7.1 <ex02.maccabiworld.org>: Helo command rejected: Host not found; from=<> to=<aiglance@mydomain.com> proto=ESMTP helo=<ex02.maccabiworld.org>

Our postfix server rejects mail like this, because it's usually spam. Properly configured mail servers shouldn't make up bogus addresses--though a few misconfigured ones do.

But where do these bogus requests come from? Do they come from specific countries? How many from .com or .org versus from specific country domains?

To find out, I'll create a Python dictionary, then use CairoPlot to plot a pie chart. Each key in the dictionary will be a top-level domain -- for example, "com"; the value will be the number of rejected messages seen from that domain.

Parsing the Log File

Filling out the dictionary means parsing /var/log/mail.info. The address each message really came from shows up in the RCPT from; get it using Python's re module. Since this is an article about CairoPlot, not Python regular expressions, just take my word for the code that follows.

#! /usr/bin/env python

import CairoPlot, re

MAIL_INFO = "/var/log/mail.info"

# Dictionary to store the results as (domain : number of rejects)
rejected = {}

# Parse mail.info to find all the 'NOQUEUE: reject' lines and
# figure out what top-level domains (TLDs) they're coming from.
f = open(MAIL_INFO)
for line in f :
if line.find('status=sent') > 0 :
pass
elif line.find('NOQUEUE: reject') > 0 :
# An attempt we rejected. Look for a pattern like
# RCPT from foo.example.com[nnn.nnn.nnn.nnn]
rcpt = re.search("RCPT from ([^[]*)[([0-9.]+)]", line)
if not rcpt :
continue
# Now rcpt.group(1) is the reverse-DNS hostname (if any)
# from the log file, rcpt.group(2) is the IP address.
if rcpt.group(1) and rcpt.group(1) != 'unknown' :
hostname = rcpt.group(1)
else :
hostname = None

# Find the part after the last "."
tld = "Unknown" # default there's no "." in the hostname
if hostname :
dot = hostname.rfind(".")
if dot >= 0 :
tld = hostname[dot+1:]
if tld in rejected :
# We've seen this TLD before; add 1.
rejected[tld] += 1
else :
# First time we've seen this TLD.
rejected[tld] = 1
f.close()

At the end of this, rejected is a dictionary suitable for passing to CairoPlot, like this:

{'ru': 3, 'ch': 1, 'ma': 2, 'rs': 2, 'it': 4, 'hu': 1, 'cz': 1, 'ar': 2, 'il': 35, 'br': 16, 'es': 1, 'co': 2, 'net': 4, 'com': 24, 'pl': 7, 'at': 2}

Generating a Pie Chart

How do you generate a pie chart from a dictionary? It only takes one line:

CairoPlot.pie_plot("piechart", rejected, 500, 500, None, True, False, None)

CairoPlot will produce a graphics file named pie.svg.

The arguments are:

pie_plot(name,
data,
width, height,
background=None,
gradient=False, shadow=False,
colors=None)

name is the filename. If you include an extension such as .jpg, CairoPlot will use that format instead of SVG format, in case you need a graphic that even IE users can view on a website.

data, of course, is the dictionary of values.

width and height are the desired size of the plot. Notice that CairoPlot leaves quite a bit of extra space around the outside of the pie, so plan accordingly.

background lets you specify a background color as a tuple of red, green and blue, so background=(0, 1, 0) would give a solid green background. You can also pass a Cairo gradient here. gradient specifies whether the pie slices themselves should show a gradient, which makes the plot prettier. shadow lets you add a drop shadow on the whole piechart, and you can pass an array of custom colors--again, tuples or gradients--if you don't like the default colors. The colors list must have exactly the same number of entries as the data dictionary.

A minor problem with the chart in we just created: It turns out most hosts with invalid HELO addresses aren't resolvable at all, and the rest of the chart gets all squinched into a tiny piece of pie. What happens if you toss out all those unknowns? You can do that by adding one else clause after the if hostname:

        if hostname :
dot = hostname.rfind(".")
if dot >= 0 :
ext = hostname[dot+1:]
else :
continue

Run that, and you get a competely different pie chat Quite interesting! I had no idea, before writing this example, that I got so much spam from Israel and Brazil compared to other countries. Sometimes a picture really is worth a thousand words.

Bar Charts

CairoPlot makes pretty bar charts, too. Unfortunately, CairoPlot's various methods aren't consistent about their input, and bar_plot wants a list, not a dictionary.

No problem! Just convert that dictionary to two lists -- one for the labels, one for the data -- and call bar_plot:

h_labels = [ k for k in rejected.keys() ]
rejlist = [ rejected[k] for k in rejected.keys() ]
CairoPlot.bar_plot ('bars', rejlist, 500, 400,
border=5, three_dimension=True,
h_labels=h_labels)

Again, you can pass a list of colors if you want custom colors, and there are a few other options available, like background, grid, rounded_corners, h_bounds and v_bounds, and of course v_labels as well as h_labels.

Of course, CairoPlot can do other types of graphs as well. There's some documentation here, or you can use the interactive Python interpreter and type

import CairoPlot
help(CairoPlot.pie_plot)

Eventually, CairoPlot may move to Sourceforge and have a more organized website. But in the meantime, if you experiment a bit, you'll find it's one of the best packages around for making pretty, colorful graphs.

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