This is a Python script which opens a KML file and rewrites each item found in the <extendeddata> section to plain attributes in the form <attributename> value </attributename>.

This makes possible to parse KML attributes with the OpenLayers.Format.KML class, which is not capable of parsing the "extendedData" section.

It is just a workaround, but it worked in my case. I hope that soon OpenLayers will extend its support for KML attributes.