Can a bash script that returns a Python interpreter replace the shebang?

Question

I've got some Python scripts that are now being run by a wide variety of folks across multiple test platforms. This creates a problem for 2 reasons:

1. The python3 path is not the same across all the testers, and
2. Not all of the people running the scripts have a path to Python set in $PATH.

Because of (1) I can't hard-code the shebang since its tester dependent and because of (2) #!/usr/bin/env python3 isn't guaranteed to work if placed at the top of Python file.

I know that the python3 interpreter is going to be in one of a few locations across the testers. So what I'm wondering, is it possible to replace the #!/usr/bin/env python3 at the top of the Python file with a call to a bash shell script that looks for the python location and then "sets" it for the script? If that's not possible, then the rest of this is moot.

I created a bash script that does look through the possible locations until it finds the interpreter, but what I don't know how to do is return it in the top of a Python file.

For example, I created a basic python file (shebang.py)

#!./pyshebang.sh

print("Hello World")

pyshebang.sh does 2 things, it appends the found python path to PATH, and echo's back that path to the interpreter. If I run the python script above, stdout gets the echo from the bash script, but not the print from the python script.

Answer 1

is it possible to replace the #!/usr/bin/env python3 at the top of the Python file with a call to a bash shell script that looks for the python location and then "sets" it for the script?

Yes, of course. That's effectively what /usr/bin/env python3 does. There's nothing magic about that particular command; it and variations on it just happen to be broadly useful.

I created a bash script that does look through the possible locations until it finds the interpreter, but what I don't know how to do is return it in the top of a Python file.

You have a misunderstanding about what's happening. A shebang line does not result in a substitution into the script. Rather, it results in the specified line being executed as a command, with the path to the original script and the arguments to it appended as an additional arguments.

Thus, your pyshebang.sh should have a general form along these lines:

#!/bin/bash
# Note: the above shebang line is not a special case

# ... find Python ...

MY_PYTHON=/the/python/I/discovered

# Execute the discovered Python, passing it all the arguments this
# script received
exec "$MY_PYTHON" "$@"