code: def workbook_data(self):
          
          document = XML(
              fn=os.path.splitext(self.fn)[0]+'.xml', 
              root=Element.workbook())
          shared_strings = [
              str(t.text) for t in 
              self.xml('xl/sharedStrings.xml')
                  .root.xpath(".//xl:t", namespaces=self.NS)]
          for key in self.sheets.keys():
              worksheet = self.sheets[key].transform(XT, shared_strings=shared_strings)
              document.root.append(worksheet.root)
          return document
docs: return a readable XML form of the data.