Turns out Print function wasn't actually being called due to different indentation type (tab vs spacing).
Python 2 seems to suffer for numbers > 10**10. while py3 has this limit around 10**12.
Also, py2 has int and long, while py3 only has 'int' which is equivalent to py2.long.

I have changed the tests to be 10**10 instead. I chose 10**10, but can't find documentation to find the real limit.
Test cases now pass except the not-implemented-yet-try-except-optimisations.
Tested exec and print using ast. Exec needed some spacing fixes.
+ Fixed minor errors.
- Ran mnfy273 on py27 stdlib.
- Fails on large numbers (pythons fault)
- Fails on specific slice e.g. "p = (p + [0,0,0,0])[:4]" returns "p = p+[0,0,0,0][:4]" which is wrong. MNFY3300 fails on this also.
I'd say mnfy273 is now fully tested.