1. I have started learning python on raspberry pi 2 board.
2. Which site is better.

3. Currently I am following:
https://pythonspot.com/python-strings/

 

The best one is probably the one that suits your personal learning style, only you know what that is.

Personally I would use a range of different resources to get different perspectives. I would also just get on and implement something that interested me and pick up what I needed as a I went along.

 

Here are some free Python eBooks that I've seen recommendations of:

• Dive Into Python - http://www.diveintopython.net/, http://www.diveintopython3.net/
• Think Python: How to Think Like a Computer Scientist - http://www.greenteapress.com/thinkpython/
• A Byte of Python - http://www.swaroopch.com/notes/python/

and there are many other resources listed on the Python wiki (for non-programmers, for programmers).

 

Try the following tutorials

http://openbookproject.net/thinkcs/python/english3e/
http://thepythonguru.com