How can I run a Python program in the global Python environment from one in a virtual Python environment?

Question

I am writing and running Python programs on a machine that I don't have much control over. The global environment has Python 3.6 installed along with dozens of packages. There are many scripts available to me in that environment that I need to be able to run.

I run most of the scripts I develop in a Python 3.9 virtual environment. It is not practical to install the dozens of packages from the Py3.6 global environment into my venv, but I do want to be able to run some of the scripts that were designed for the 3.6 environment from my own 3.9 scripts.

I don't need to interact with the 3.6 script I'm running. I want to print the output as it is generated, and then process any files it produces.

This is basically what I want to do, although it doesn't actually work:

def run36 (scriptname):
    p = subprocess.Popen("deactivate;", "python3", scriptname, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True, bufsize=1, universal_newlines=True)
    for l in p.stdout():
        print(l.rstrip())
    return p.returncode

run36("some36prog.py")  # will generate somenewfile.txt
with open("somenewfile.txt") as f:
    ...

If the correct answer is that I need to explicitly call the Python3.6 executable to make this work, I need to be able to discover its path somehow without hard coding it.

Answer 1

Just use the absolute path to the global interpreter. Or, if you just need the python version, create another virtualenv and use the interpreter in there.

For example

# create a Python3.6 virtualenv
python3.6 -m venv venv36

# use the python3.6 interpreter from code running with python3.12
python3.12 -c "import subprocess; subprocess.run(['venv36/bin/python', 'some_script.py'])"