For the operating system to understand that the file should be read as a Python program, the programmer needs to save the file as a Python file, with the ".py" extension. In Notepad, ...

If you then save the file as “.CSV” then it will open in Excel when you click on it! ... For example, if you want to write a .Doc file in Python, you’ll come unstuck!

The problem I've noticed is that if I append the file with each of the 100k runs (one at a time), it can happen that two threads try to save to the file at the same time and some row(s) end up empty.