A simple python web server for returning live data from the London Underground. Example request: /B/BST/1

london-underground.py

'''
The MIT License (MIT)

Copyright (c) 2014 Maciej Goszczycki

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
'''

import xml.dom.minidom as dom
import urllib2
import time
import flask

# Global cache
cache = {}
cacheDuration = 60 #sec

# Get URL Content
def getPlatform(line, station, platformno):
    # Handle caching
    global cache
    cacheString = "{}/{}/{}".format(line, station, platformno)
    cached = cache.get(cacheString, {})
    if cached and cached['time'] + cacheDuration >= time.time():
        print("'{}' cached at {}, returning".format(cacheString, cached['time']))
        print("Current itme: {}".format(time.time()))
        return cached['data']

    # Make new request if caching failed
    print("Missing or old cache making new request for {}".format(cacheString))
    url = "http://cloud.tfl.gov.uk/TrackerNet/PredictionDetailed/{}/{}"
    response = urllib2.urlopen(url.format(line, station))
    xml = dom.parseString(response.read())
    platformtrains = xml.getElementsByTagName('P')[platformno]

    # Travserse the DOM
    trains = map(lambda e: lambda v: e.attributes[v].value, platformtrains.getElementsByTagName('T'))
    stname = xml.getElementsByTagName('S')[0].attributes['N'].value[:-1] #Remove the dot from the name
    linename = xml.getElementsByTagName('LineName')[0].firstChild.nodeValue
    platform = platformtrains.attributes['Num'].value

    # Assign cache
    data = (linename, stname, platform, trains)
    cache[cacheString] = {'time': time.time(), 'data': data}
    return data

# Create the Flask app
app = flask.Flask(__name__)

# Route for retriving platforms
@app.route('/<line>/<station>/<int:platform>')
def handlePlatform(line, station, platform):
    # Train data
    linename, stname, platform, trains = getPlatform(line, station, platform)
    # Markup
    header = "<h1>Trains on platfrom {}, on station {}, on line {}</h1>".format(platform, stname, linename)
    tablepre = "<table><tr><th>Destination</th><th>Time to</th></tr>"
    tablepost = "</table>"

    # Produce the HTML
    html = header + tablepre
    for train in trains:
        html += "<tr><td>{}</td><td>{}</td><tr>".format(train('Destination'), train('TimeTo').replace('-', '<i>Due</i>'))
    html += tablepost
    return html


# Start the server at :1024
if __name__ == "__main__":
    app.run(port=1024, debug=True)