I guess you're talking about the xlsx file format that was introduced with Excel 2007?
xlrd and xlwt don't support it yet, but there's some initial work in xlrd (
https://github.com/python-excel/xlrd ) towards reading xlsx files in a future release. If you're preparing files to open in Excel, you can keep writing xls files with xlwt, because new versions of Excel should still be able to open them.
You could also look at openpyxl, which is written for working with xlsx files:
http://pypi.python.org/pypi/openpyxlThomas