12.2. Web services

The term web service has a number of meanings, depending on whom you ask. The simplest is that a web service is a way for a program on one computer to use HTTP (and hence the web) to ask another computer for some information or to ask it to perform some action. The key idea is that the information that comes back in response is structured to be useful to a computer program, rather than the jumbled HTML of a normal web page with navigation, advertising, script code, and content all mixed together. The format of the information could be anything; commonly used formats are XML (particularly RSS, Atom, and SOAP), JavaScript Object Notation (JSON), and good-old plain text. Python’s strong string-handling capabilities come in very handy when dealing with all of these different formats, and often libraries are available to do the parsing for us.

In section 12.2 we look at three different kinds of web service. To begin, we see an example of one of the simplest: the feed of recent articles from a weblog. The code for using this service makes exactly the same kind of request a web browser makes for web pages, but it processes the information it gets back rather than displaying it directly to the user. In section 12.2.2 we look at using SOAP web services, which have a different way of packaging up requests and responses. The .NET framework has some tools that make SOAP services very convenient to use. Then in the last part of the chapter we explore how we can build our own web service using the REST architectural style.