Python 3.5 problem

ok I HAVE looked to see if this has been asked and it hasn't 'quite'.

Firstly hello and thank you for taking the time to look at this.

ok I'm hoping to lea Python 3.5 (I'm completely new to programming btw) so I write the traditional 'Hello World' in Kate and save it to Documents/Progs as 'helloworld.py' - in ths file which I created for my Pythin 3.5 programs. I cd to this directory from the terminal and for the life of me I can't get this to open or run. I either get a 'file not found' error or I get 'syntax error'.

Now I think whats happening is that the terminal defaults to 2.7 which would explain the syntax error. If I open the terminal and type 'Pythin3.5' to begin with I get the usual '>>>' and can write in Python 3.5 BUT I can't then save the file.

So I need the thing to recognise the syntax of 3.5 programs written in Kate because I'm never going to write in 2.7.

So the questions are:

1. How do I get the terminal (Konsole) to recognise P3.5 files that I write in Kate and save in the said directory?
2. Can I write in P3.5 in the terminal and save it from there - and if so will I still have the same prob?

I realise that the 'helloworld.py' file is very basic but I simply caot move on without knowing how to open my saved programs with 3.5.

If someone could do the Touron Rah for me, I would appreciate it

Thanks for reading.

Kubuntu 16.04 - which I believe to be the most advanced OS on earth. Genius pure and simple