How to format python interpreter text?

Question

I am trying to edit the text that pops up when I launch the python3 interpret. This should be a very simple task and I am trying to use the PYTHONSTARTUP environment variable set to a file .pythonrc.py but I am not 100% sure what I am doing. For some reason I cannot find a simple script that shows how this is done. I do not have my own generated code because I didn't even write the code for my terminal customization. I just googled how to edit, found some examples and then tweeked it from there.

I just want to know how to change this.

Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 03:03:55) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

Answer 1

$ python -i -c "print('my own banner')"
my own banner
>>>