I modified a module that uses elementtree to work with lxml. Most of the changes required adjusting for the documented differences between elementtree and lxml. There was one difference in output, however, that was a little idiosyncratic. Using the following XML document: <rss version="2.0"> <channel> <title>Example</title> <link>http://www.example.org/</link> <description>RSS Example</description> <language>en-us</language> <pubDate id="cpubdate">$month $day, $year</pubDate> <lastBuildDate id="lastbuilddate">%(month)s %(day)s, %(year)s</lastBuildDate> <item class="item"> <title id="title" /> <link id="link" /> <guid id="guid" isPermaLink="true" /> <description id="description" /> <pubDate id="ipubdate" /> </item> </channel> </rss> I modified the element: <guid isPermaLink="true" id="guid"/> by adding an attribute consisting of name: '{http://www.w3.org/1999/02/22-rdf-syntax-ns#}resource' and value 'http://www.example.com/rss/5423093' through (internally) a call to the guid element's set method. Prior to this call, there were no namespaces declared in the document. After the call, in both the elementtree and lxml implementations, the guid element is modified to look like this: <guid xmlns:ns0="http://www.w3.org/1999/02/22-rdf-syntax-ns#" isPermaLink="true" id="guid" ns0:resource="http://www.example.com/rss/5423094"/> When I delete the attribute using (internally) the statement: del guid.attrib['{http://www.w3.org/1999/02/22-rdf-syntax-ns#}resource'] with the elementtree version the result looks like this: <guid id="guid" isPermaLink="true" /> while with the lxml version the result looks like this: <guid xmlns:ns0="http://www.w3.org/1999/02/22-rdf-syntax-ns#" isPermaLink="true" id="guid"/> Any ideas on why the namespace declaration lingers in the lxml output? Thanks, L.C. Rees lcrees@gmail.com