Python Cookbook

Module: Fetching Latitude/Longitude Data from the Web

Credit: Will Ware

Given a list of cities, Example 11-1 fetches their latitudes and longitudes from one web site (http://www.astro.ch, a database used for astrology, of all things) and uses them to dynamically build a URL for another web site (http://pubweb.parc.xerox.com), which, in turn, creates a map highlighting the cities against the outlines of continents. Maybe someday a program will be clever enough to load the latitudes and longitudes as waypoints into your GPS receiver.

The code can be vastly improved in several ways. The main fragility of the recipe comes from relying on the exact format of the HTML page returned by the http://www.astro.com site, particularly in the rather clumsy for x in inf.readlines( ) loop in the findcity function. If this format ever changes, the recipe will break. You could change the recipe to use htmllib.HTMLParser instead, and be a tad more immune to modest format changes. This helps only a little, however. After all, HTML is meant for human viewers, not for automated parsing and extraction of information. A better approach would be to find a site serving similar information in XML (including, quite possibly, XHTML, the XML/HTML hybrid that combines the strengths of both of its parents) and parse the information with Python’s powerful XML tools (covered in Chapter 12).

However, despite this defect, this recipe still stands as an example of the kind of opportunity already afforded today by existing ...