I'm using Odoo online and my website is in a domain like .odoo.com

Hi I'm just starting with Odoo, when I search something about a change I'd like to make in my app I see that people edit the source code, so far I've been able to edit the XML code of the views and templates but I can't find where to edit the python code, I know that this is simple when you have installed odoo in a local machine and clone the repos but it is possible to do it with the online version?

Thank you for everything