crontab_example.py

#!/path/to/the/python/interpreter/in/virtualenv
# -*- coding: utf-8 -*-

import subprocess
import sys

def main():
  try:
    subprocess.call("echo 'Hello!'", shell = True)
    sys.exit(0)
  except Exception as e:
    print(e, file = sys.stderr)
    sys.exit(1)

if __name__ == "__main__":
  main()