i don't know much about cron but thought that was to schedule tasks once the system was up and running
IN slackware (which didn't use systemd) for evoking stuff at boot up you could put scripts at /etc/rc.d/rc.local
haven't a clue how to do that with systemd
with python either the script is going to be needed to be evoked with something like : sudo python yourPythonScript.py or you compile an executable elf , which is what 've done for a Arch AUR program(installed to /usr/bin) even then it needs to be evoked from command line : sudo nameOfElf