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Python & XML by Christopher A. Jones, Fred L. Drake

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Connecting with HTTP

While urllib is suitable for working with Internet files, you may still have the need to perform more intricate communication with an HTTP server. For example, if you are writing a Python program to communicate between two web sites, you may need to adjust the headers to include any cookies the site may require. You may need to emulate a certain browser type (by placing its name in your User-Agent header) if the site requires the latest version of Internet Explorer. Working with httplib as opposed to urllib in cases such as these allows for finer control.

HTTP Conversations

HTTP conversations between browsers and servers involve headers and data. The interaction between a web browser and a web server reveals a great deal of information about both parties. The HTTP headers that precede content from the server and precede requests from the browser contain a lot of metadata about both client and server. For example, when you type a URL into your browser and press return, a complete HTTP request is sent to the remote server that can look something like this:

GET /c7/favquote.cgi HTTP/1.1
Host: www.python.org
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg
Accept-Language: en-us
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.5; Windows 98; Win 9x 4.90)
Connection: Keep-Alive

The headers tell the web server a great deal about the capabilities of the client browser. From the first line of the headers (GET /c7/favquote.cgi HTTP/1.1 ...

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