This tutorial is a good starting point; the below notes relate specifically to running a python script from within a user's anaconda environment on boot.

First, choose a preferred location for your script, for example:

mkdir -p ~/systemd/

In ~/systemd/service.py:

import time
import datetime

def main():
    while True:
        print(datetime.datetime.now())
        time.sleep(10)

if __name__ == '__main__':
    main()

Next, include the following in ~/systemd/on_start.sh:

#!/bin/bash
source $HOME/miniconda3/etc/profile.d/conda.sh
conda activate base # change to your conda environment's name
# -u: unbuffered output
python -u $HOME/systemd/service.py

In order to run the source command, specifying bash is necessary. You might need to change miniconda3 to anaconda3 depending on your conda installation (see here for details). Consult this for details on unbuffered output.

Then chmod +x ~/systemd/on_start.sh and test it.

In ~/.config/systemd/user/example.service (note, that's the word user, not your username):

[Unit]
Description=Example Python Service

[Service]
Type=simple
WorkingDirectory=/home/ubuntu/systemd/
ExecStart=/home/ubuntu/systemd/on_start.sh

[Install]
WantedBy=default.target

Note that this specifies a working directory. You should now see example.service listed when running systemctl --user list-unit-files.

To test:

systemctl --user enable example.service
systemctl --user start example.service

Run journalctl --user-unit example.service (or tail -f /var/log/syslog) to observe output, and inspect status with systemctl --user status example.service.

Note: You can tail the output of journalctl with the -f flag: journalctl --user-unit example.service -f

To run the service on boot, without requiring the user to login:

sudo loginctl enable-linger $USER

This can be undone with sudo loginctl disable-linger $USER, and status can be queried via this command: ls /var/lib/systemd/linger.

To stop the service and prevent it from running on boot:

systemctl --user stop example.service
systemctl --user disable example.service