In first attempt there are two things that make incompatible with older version:
- Exception handling 
   This cause first syntax error on 2.4.4, because that version has not 
         "except <ExceptionClass> as <variable>:" 
   form. It has "except <ExceptionClass>:" only and the other information can be read from special variables of "sys" module. 
- CLI argument parsing
    The 2.4.4. has "optparse" module instead of "argparse" with different syntax.

As Richard told earlier Python 3 is a different language. To represent the difference there is an official source code translator form 2.x to 3.x.