I have just done a similar thing and worked trough
https://www.learnpython.org/ after wanting to do some Python for many years now. And I found it quite good.
Next I would suggest to take on a real project, creating a small program that you can use for a task you always wanted to have solved. That way you will apply the things you just learned from the tutorial and quickly encounter situations that were not covered at all.
https://docs.python.org/3/ will be your friend in that case. Of course you'll always find a lot of tipps and suggestions on
https://stackoverflow.com/ too. Just don't start to blindly copy code from there that you do not understand! Otherwise it can be a great ressource.
By the way. Everything above is pretty valid for any programming lanuguage you want to learn, but your interest is Python and that's well enough.
Now to the mobile part. Forget it - seriously!
I have even tried to do some Python (as well as other languages) on Android just to see if it is possible. If you really want to do that, I would point you to
https://termux.com/ in that case. Install it first and then get your favourite commandline editor (vim, emacs etc) as well as python by using termux's "pkg" packet management. You'll have a full blown Python environment and are ready to go but what next? You're stuck to a tiny screen and need an external keyboard for any serious input.
Sure, it can be done and if you're able to pull of any productive work with a setup like that, I'll be your biggest fan forever. But mobile devices (and operating systems) are made to be pure consumption machines and not for productivity. Get a real computer, even if it is only a Raspberry Pi with an USB keyboard and mouse, connected to your TV. That will enable you to have the python docs and your editor visible next to each other at the same time, imagine that possibility!
Since these are the Pyra boards, Pyra will be much better suited for coding because it has a keyboard with all important characters easily reachable (yay, keyboard thread!). I do plan to install "everything" programming related that I can imagine. Still, I do not think it will be really suitable for anything more than hacking together small scripts, do a quick bugfix or reconfigure your webserver while you are on the go. Not because it couldn't, but because of the small screen. Connect it o external keyboards, screen etc.. and it will blow away above Raspi setup for sure