I only done coding in 2.7 of python os it sufficient for gaining mastery in python,should i work in 3x version

Answer 1

yes you need to work on 3x version because now days no anyone use python 2.7 version it is old.python 3x has some new features which you can learn in only 1 month or may be 15-20 days.

Answer 2

All new development will be done on 3.x and libraries will start to no longer be compatible with 2.7 so yes switching to 3.x is a good idea