Distinguishing between when a script is ran 'directly', or with Python executable

Question

How can a Python program determine if it was executed as an executable file on a Unix system instead of being called as a script?

./program.py

instead of

python ./program.py

'/program' in sys.argv[0] cannot distinguish between the example cases.

Answer 1

A somewhat hackish solution would be adding an environment variable indicating this to the shebang line in program.py:

#!/usr/bin/env noscript=True python
import os
if os.getenv('noscript'):
    print("called as executable")
else: 
    print("called as script")