12.3 Other Language Changes

• The raise statement now takes an optional argument which specifies the traceback to be used when printing the exception's stack trace. This must be a traceback object, such as found in sys.exc_traceback. When omitted or given as None, the old behavior (to generate a stack trace entry for the current stack frame) is used.
• The tokenizer is now more tolerant of alien whitespace. Control-L in the leading whitespace of a line resets the column number to zero, while Control-R just before the end of the line is ignored.