Python calling subprocess that requires no virtual environment

Question

I have a Python 3.6 script that calls out to a third-party tool using subprocess.

main_script.py:

#!/usr/bin/env python
import subprocess
result = subprocess.run(['third-party-tool', '-arg1'], shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

The problem is, main_script.py must be run from within a virtual environment, and third-party-tool must be run from no virtual environment whatsoever.

I don't know much about third-party-tool, except that it is on my path. Calling it while I have a virtual environment active causes it to jam up and throw an exception later on. I do not know if it uses the default python binary or it it spins up its own virtual env and does stuff in there. It is not a Python script, but apparently calls one somehow.

How do I tell subprocess to drop out of my virtual environment and run the command in the default shell environment?

I've examined a couple of similar questions:

• Running subprocess within different virtualenv with python -- In the first case, they are specifying the environment by calling their script with a specific version of Python. third-party-tool is not a Python script (I believe it's bash).
• Python subprocess/Popen with a modified environment -- In the second case, they're tweaking existing environment variables, which looks promising, but I want to reset to the default environment, and I'm not sure if I necessarily know which variables I need to clear or reset.

Answer 1

From the documentation of subprocess:

https://docs.python.org/3/library/subprocess.html

The accepted args are

subprocess.run(args, *, stdin=None, input=None, stdout=None, stderr=None,
    capture_output=False, shell=False, cwd=None, timeout=None, check=False,
    encoding=None, errors=None, text=None, env=None, universal_newlines=None)

In particular,

If env is not None, it must be a mapping that defines the environment variables for the new process; these are used instead of the default behavior of inheriting the current process’ environment. It is passed directly to Popen.

Thus, passing an empty dictionary env={} (start with empty environment) and using bash --login (run as login shell, which reads env defaults) should do the trick.

subprocess.run(['bash', '--login', '-c', '/full/path/to/third-party-tool', '-arg1'], shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env={})