Pitted Knowledge of the Almighty Olive: Parsing XML with Google App Engine: Python

This is a continuation of my Python 2.7 and Google App Engine series. If you are just starting out I suggest you start reading Getting Started and First App.

In this example we are going to read an XML document, parse it and then display it as a HTML table.

The XML document

The following code example came from a job I was doing interfacing a web application with GeoOP, a dispatch and a mobile workforce management system. They have an API but I have 'sanitized' my code to protect IP. But it is a really good system, and if you need something like it I suggest you pop on over and take a peek.

So everyone else can use the code, I've modified my code to use a publicly available XML source available from http://data.gov.au/data/. Specifically, I am using the list of ABC local radio stations.

The code

I am not going to bother explaining how to set up a project environment since I have explained it in earlier blog posts (see the first paragraph). Create a new python file (ensure your YAML configuration file is set correctly) and add the following:

# The webapp2 framework
import webapp2

# The URL Fetch library
from google.appengine.api.urlfetch import fetch

# The minidom library for XML parsing
from xml.dom.minidom import parseString

# Fetches an XML document and parses it
class MainPage(webapp2.RequestHandler):
    # Respond to a HTTP GET request
    def get(self):
        # A try-catch statement
        try:
            # Grabs the XML
            url = fetch('http://www.abc.net.au/local/data/public/stations/abc-local-radio.xml')

            # Parses the document
            xml = parseString(url.content)

            # Sets up the webpage
            self.response.out.write("<html><body><table>")

            # Outputs the table
            self.response.out.write(outputHTML(xml))

            # Sets up the webpage
            self.response.out.write("</table></body></html>")

        # Our exception code
        except (TypeError, ValueError):
            self.response.out.write("<html><body><p>Invalid inputs</p></body></html>")

# Output the XML in a HTML friendly manner
def outputHTML(xml):
    # The get the states list
    states = xml.getElementsByTagName("state")

    # Our return string
    outputString = ""

    # Cycled through the states
    for state in states:
        #Gets the stations and cycle through them
        stations = state.getElementsByTagName("station")
        for station in stations:
            # Grab data from the station element
            stationname = station.getElementsByTagName("stationname")[0].firstChild.data
            town = station.getElementsByTagName('town')[0].firstChild.data
            website = station.getElementsByTagName('website-url')[0].firstChild.data

            # Append the data onto the string
            string = "<tr><td>" + str(stationname) + "</td><td>" + str(town) + "</td><td>" + str(website) + "</td></tr>"
            outputString+=string

    # Output string
    return outputString

# Create our application instance that maps the root to our
# MainPage handler
app = webapp2.WSGIApplication([('/*', MainPage)], debug=True)

If you set it up correctly then you should see a list of ABC radio stations!

References

Google's own getting started with webapp and Python.
The office webapp2 reference
The Google developer resource for the App Engine
Google App Engine FAQs
"URL Fetch API, minidom (Google App Engine)" by kahara
minidom reference material

Pitted Knowledge of the Almighty Olive

Jun 7, 2012

Parsing XML with Google App Engine: Python

The XML document

The code

References

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