[Tutor] Program to check Python 2 syntaxes incompatible to Python 3?

[STF]

Hi,

After reading some articles about Python 2 vs Python 3 issues and web pages
like:
https://docs.python.org/3/whatsnew/3.0.html
https://wiki.python.org/moin/Python2orPython3

I'm wondering if there's any program/tool to list out incompatible syntaxes
in a Python 2 source file.

I know the 2to3 tool exists, but I'm more interested to do some manual
change to source code if possible.

Thanks in advance.