On the 'Edit and Run Programs' page I showed you how to create a Python file and edit it within the internal text editor of MobaXTerm personal Edition. MobaXTerm is for Windows only but I'm guessing there are equivalent programs for Mac and Linux. A text editor CAN be used to create Python programs but it's better to use an integrated development environment (IDE) because an IDE offers extra features such as debugging and autocomplete.
According to my research, the best free Python IDE for beginners is probably PyCharm Edu. This program is available for macOS, Windows and Linux. As the name suggests, this IDE is designed for learners - it includes the possibility of working through Python lessons with fill-in-the-blank type exercises and indeed a good introductory course is included in the package. Also, PyCharm Edu gives you an easy upgrade path to the paid-for version of PyCharm which is very popular with professional Python programmers. PyCharm Edu can be downloaded HERE.
It's very easy to configure MobaXTerm personal edition so that double-clicking a Python file automatically opens it in PyCharm Edu. Saving the file will automatically save the file back to the brick. Just choose Settings>Configuration>General to get the following dialog:
Then click the little blue square at the right of the 'default text editor program' box and navigate to the pycharm.exe file on your computer. It's as simple as that! Now, every time you double-click a file in MobaXTerm's directory listing it will open in PyCharm Edu and when you save the file it will save straight back to the EV3 brick.
It's important NOT to use MobaXTerm to make new Python files for the brick since it would be hard to make them directly on the brick or to move them to the brick alter. If you want to make a new Python file on the EV3 then simply click the 'New File' icon at the top of MobaXTerm's directory listing panel and give the new file a name ending in .py, such as myfile.py. Then you can open the new file by double-clicking and get to work editing it in PyCharm Edu!