interchangeable shebang line in Python script for dual OSes?

Question

A script is developed both on OS X and Windows using a virtualenv. The so-called developer has already installed all required packages using a requirements.txt file, but one problem remains:

If the script is running on OS X, the beginning of each Python file must start like this:

#!/Users/os-x-username/.virtualenvs/some_env/bin/python
#!C:\Users\windows-username\Envs\some_env\Scripts\python.exe

But if developing on Windows, the line order must be switched:

#!C:\Users\windows-username\Envs\some_env\Scripts\python.exe
#!/Users/os-x-username/.virtualenvs/some_env/bin/python

How can the so-called developer avoid this tediousness?

Answer 1

If you don't mind adding extra steps, ou can create a launcher script launcher.py like:

#!/usr/bin/env python

import subprocess
import sys

if __name__ != "__main__":
    print("This is a launcher. Please run only as a main script.")
    exit(-1)

INTERPRETERS = {
    "win": r"C:\Users\windows-username\Envs\some_env\Scripts\python.exe",  # Windows
    "darwin": "/Users/os-x-username/.virtualenvs/some_env/bin/python",  # OSX
    "linux": "/home/linux-user/.virtualenvs/some_env/bin/python"  # Linux
    # etc.
}

TARGET_SCRIPT = "original_script_name.py"

interpreter = None
for i in INTERPRETERS:  # let's find a suitable interpreter for the current platform
    if sys.platform.startswith(i):
        interpreter = i
        break
if not interpreter:
    print("No suitable interpreter found for platform:", sys.platform)
    exit(-1)

main_proc = subprocess.Popen([interpreter, TARGET_SCRIPT] + sys.argv[1:])  # call virtualenv
main_proc.communicate()  # wait for it to finish

exit(main_proc.poll())  # redirect the return code

Since this script is there only to run the original_script_name.py in the desired interpreter for the current platform, it doesn't matter what its shebang is - as long as it picks any Python interpreter it will be fine.

It would act as a drop-in replacement for your original script (original_script_name.py) so just call launcher.py instead and it will even redirect the CLI arguments if needed.