Below you can find a code snippet for parallel jobs in python.

So what does delayed exactly do? If you exclude it it will just run in 10 seconds. It seems like everything was run in the main thread! And that is exactly what happened. The delay makes sure that python halts the excution of my_fun and first orders all the tasks and then executes them parallel.

So unfortunately there are instances where parallel doesn’t work because of how stuff is executed behind the scenes. This is the case for the neural network packages. You will have to do extra work to get those to run parallel.