Chapter 12. SOAP Web Services

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.

12.1. Diving In

You use Google, right? It's a popular search engine. Have you ever wished you could programmatically access Google search results? Now you can. Here is a program to search Google from Python.

Example 12.1. `search.py`

from SOAPpy import WSDL

# you'll need to configure these two values;
# see http://www.google.com/apis/
WSDLFILE = '/path/to/copy/of/GoogleSearch.wsdl'
APIKEY = 'YOUR_GOOGLE_API_KEY'

_server = WSDL.Proxy(WSDLFILE)
def search(q):
    """Search Google and return list of {title, link, description}"""
    results = _server.doGoogleSearch(
        APIKEY, q, 0, 10, False, "", False, "", "utf-8", "utf-8")
    return [{"title": r.title.encode("utf-8"),
             "link": r.URL.encode("utf-8"),
             "description": r.snippet.encode("utf-8")}
            for r in results.resultElements]

if __name__ == '__main__':
    import sys
    for r in search(sys.argv[1])[:5]:
        print r['title']
        print r['link']
        print r['description']
        print

You can import this as a module and use it from a larger program, or you can run the script from the command line. On the command line, you give the search query as a command-line argument, and it prints out the URL, title, and description of the top five Google search results.

Here is the sample output for a search for the word “python”.

Example 12.2. Sample Usage of `search.py`

C:\diveintopython\common\py> python search.py "python"
<b>Python</b> Programming Language
http://www.python.org/
Home page for <b>Python</b>, an interpreted, interactive, object-oriented,
extensible<br> programming language. <b>...</b> <b>Python</b>
is OSI Certified Open Source: OSI Certified.

<b>Python</b> Documentation Index
http://www.python.org/doc/
 <b>...</b> New-style classes (aka descrintro). Regular expressions. Database
API. Email Us.<br> docs@<b>python</b>.org. (c) 2004. <b>Python</b>
Software Foundation. <b>Python</b> Documentation. <b>...</b>

Download <b>Python</b> Software
http://www.python.org/download/
Download Standard <b>Python</b> Software. <b>Python</b> 2.3.3 is the
current production<br> version of <b>Python</b>. <b>...</b>
<b>Python</b> is OSI Certified Open Source:

Pythonline
http://www.pythonline.com/


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