Chapter 11 focused on document-oriented web services over HTTP. The “input parameter” was the URL, and the “return value” was an actual XML document which it was your responsibility to parse.

This chapter will focus on SOAP web services, which take a more structured approach. Rather than dealing with HTTP requests and XML documents directly, SOAP allows you to simulate calling functions that return native data types. As you will see, the illusion is almost perfect; you can “call” a function through a SOAP library, with the standard Python calling syntax, and the function appears to return Python objects and values. But under the covers, the SOAP library has actually performed a complex transaction involving multiple XML documents and a remote server.

SOAP is a complex specification, and it is somewhat misleading to say that SOAP is all about calling remote functions. Some people would pipe up to add that SOAP allows for one-way asynchronous message passing, and document-oriented web services. And those people would be correct; SOAP can be used that way, and in many different ways. But this chapter will focus on so-called “RPC-style” SOAP -- calling a remote function and getting results back.