Clearly you are not a python developer. This isn't correct at all. First, there is nearly nothing to relearn if you target 2.7.

http://docs.python.org/3/howto/pyporting.html#use-same-sourc...

Second, most software of any complexity will have dependencies. Although progress has been made, several packages that many projects depend upon are still red:

http://python3wos.appspot.com/