Mac slowing down / working in burst mode at night (while running Python script)

Question

This question concerns a MacBook Pro 2021, MacOS 13.6.3.

I am running a python script that reads data from a file on the hard disc, makes a 8192*8192 matrix, finds its eigenvalues and saves some of them to disc, looped over a few thousand files.

During the day, when the display is on or off, each loop iteration takes about 10 seconds.

However at night the script slows right down and works in bursts: it goes through a handful (4-6) loop iterations at 10 sec each, then "rests" for 10-20 minutes, then does another burst.

I have set System Settings > Displays > Advanced > "Prevent automatic sleeping on power adapter when the display is off" to on, so it shouldn't be sleeping.

I am like ~80% sure that this wasn't happening before I updated from MacOS 12.

What could be causing this slowdown/burst mode at night, and how can I stop it?

• TheNextman: App Nap?
• jms547: It could be. It certainly shows the symptoms of being impacted by App Nap. I'll try to disable it next time I run the python script. Thanks!