Do not mix spaces and tabs. PEP8 says to use spaces. Convert your tabs to 4 spaces (again, from PEP8). Here is a decent discussion on the thoughts behind spaces vs tabs.
Therefore, it is generally a good idea not to mix tabs and spaces for indentation. If you use tabs only or spaces only, you're fine.
Furthermore, it can be a good idea to avoid tabs alltogether, because the semantics of tabs are not very well-defined in the computer world, and they can be displayed completely differently on different types of systems and editors. Also, tabs often get destroyed or wrongly converted during copy&paste operations, or when a piece of source code is inserted into a web page or other kind of markup code.