How can I determine if a python script is executed from crontab?

I would like to know how can I determine if a python script is executed from crontab?

I don't want a solution that will require adding a parameter because I want to be able to detect this even from an imported module (not the main script).

Not quite what you asked, but maybe what you want is sys.stdout.isatty(), which tells if stdout is connected to (roughly speaking) a terminal. It will be false if you pipe the output to a file or another process, or if the process is run from cron.