@pinakinnayi : thank you for the reply, yes i have done the same thing already actually my question is how to write that into a new file and ask the user where to save same like pdf report where it shows the dialog box to save it into the disk ???

The steps i followed ..... python code :

class xmlFile_Creation(osv.osv):  
#this function "generate_xml " is called from button click on view.xml and stores the encoded xml data into database coloumn
    def generate_xml(self,cr, uid, ids, context=None):
        root = ET.Element("root")
        doc = ET.SubElement(root, "doc")                
        field1 = ET.SubElement(doc, "field1")
        field1.set("name", "blah")
        field1.text = "some value1"        
        field2 = ET.SubElement(doc, "field2")
        field2.set("name", "asdfasd")
        field2.text = "some vlaue2"        
        xmlstr = ET.tostring(root)            
        file=base64.encodestring( xmlstr )
        return self.write(cr, uid, ids, {'filedata':file, 'name':"filenew"}, context=context)          
    _name="sample.xmlfile.creation"
    _columns={
              'trader':fields.many2one('sample.traders','SelectTrader'),
              'name': fields.char('Filename', 16, readonly=True),
              'filedata': fields.binary('File', readonly=True), 
              }
xmlFile_Creation()