@dishant_18 it all depends on what you want to do with Python. First about Python 2 vs Python 3 read this, and as stated here “Python 2.x is legacy, Python 3.x is the present and future of the language”. There are only a few changes to the Python 2 syntax in Python 3 along with a bunch of new features.
When it comes to competitive programming however, they function pretty much the same. I use Python 3, and I didn’t learn it from any particular site, just the Python docs and Google searches for something particular when required. It’s a simple language so I don’t think anything more is necessary. The primary upside to using Python is a lot less typing :D, because there are so many features that make it easy to use. The downside is the slow speed, and a very specific thing which is the absence of a sorted set/map.
PyPy is a fast implementation of Python, so it is surely the best choice of Python compiler for competitive programming. As of now CodeChef does not support the PyPy compiler for Python 3 so if you use PyPy you have to write Python 2 code.
@phben is one of the best programmers here who I have noticed regularly uses Python. You can see his solutions if you like. There’s also @mathecodician and myself who often use Python. That’s it, and good luck!