last_type

These three variables are not always defined; they are set when an exception is not handled and the interpreter prints an error message and a stack traceback. Their intended use is to allow an interactive user to import a debugger module and engage in post-mortem debugging without having to re-execute the command that caused the error. (Typical use is "import pdb; pdb.pm()" to enter the post-mortem debugger; see the The Python Debugger, chapter for more information.)

The meaning of the variables is the same as that of the return values from sys.exc_info. (Since there is only one interactive thread, thread-safety is not a concern for these variables, unlike for exc_type etc.)