Is it possible to change the Environment of a parent process in Python?
Question:
In Linux When I invoke python from the shell it replicates its environment, and starts the python process. Therefore if I do something like the following:
import os
os.environ["FOO"] = "A_Value"
When the python process returns, FOO, assuming it was undefined originally, will still be undefined. Is there a way for the python process (or any child process) to modify the environment of its parent process?
I know you typically solve this problem using something like
source script_name.sh
But this conflicts with other requirements I have.
Answers:
It’s not possible, for any child process, to change the environment of the parent process. The best you can do is to output shell statements to stdout that you then source, or write it to a file that you source in the parent.
No process can change its parent process (or any other existing process’ environment).
You can, however, create a new environment by creating a new interactive shell with the modified environment.
You have to spawn a new copy of the shell that uses the upgraded environment and has access to the existing stdin, stdout and stderr, and does its reinitialization dance.
You need to do something like use subprocess.Popen to run /bin/bash -i.
So the original shell runs Python, which runs a new shell. Yes, you have a lot of processes running. No it’s not too bad because the original shell and Python aren’t really doing anything except waiting for the subshell to finish so they can exit cleanly, also.
I would use the bash eval statement, and have the python script output the shell code
child.py:
#!/usr/bin/env python
print 'FOO="A_Value"'
parent.sh
#!/bin/bash
eval `./child.py`
I needed something similar, I ended up creating a script envtest.py with:
import sys, os
sys.stdout = open(os.devnull, 'w')
# Python code with any number of prints (to stdout).
print("This is some other logic, which shouldn't pollute stdout.")
sys.stdout = sys.__stdout__
print("SomeValue")
Then in bash:
export MYVAR=$(python3 envtest.py)
echo "MYVAR is $MYVAR"
Which echos the expected: MYVAR is SomeValue
In Linux When I invoke python from the shell it replicates its environment, and starts the python process. Therefore if I do something like the following:
import os
os.environ["FOO"] = "A_Value"
When the python process returns, FOO, assuming it was undefined originally, will still be undefined. Is there a way for the python process (or any child process) to modify the environment of its parent process?
I know you typically solve this problem using something like
source script_name.sh
But this conflicts with other requirements I have.
It’s not possible, for any child process, to change the environment of the parent process. The best you can do is to output shell statements to stdout that you then source, or write it to a file that you source in the parent.
No process can change its parent process (or any other existing process’ environment).
You can, however, create a new environment by creating a new interactive shell with the modified environment.
You have to spawn a new copy of the shell that uses the upgraded environment and has access to the existing stdin, stdout and stderr, and does its reinitialization dance.
You need to do something like use subprocess.Popen to run /bin/bash -i.
So the original shell runs Python, which runs a new shell. Yes, you have a lot of processes running. No it’s not too bad because the original shell and Python aren’t really doing anything except waiting for the subshell to finish so they can exit cleanly, also.
I would use the bash eval statement, and have the python script output the shell code
child.py:
#!/usr/bin/env python
print 'FOO="A_Value"'
parent.sh
#!/bin/bash
eval `./child.py`
I needed something similar, I ended up creating a script envtest.py with:
import sys, os
sys.stdout = open(os.devnull, 'w')
# Python code with any number of prints (to stdout).
print("This is some other logic, which shouldn't pollute stdout.")
sys.stdout = sys.__stdout__
print("SomeValue")
Then in bash:
export MYVAR=$(python3 envtest.py)
echo "MYVAR is $MYVAR"
Which echos the expected: MYVAR is SomeValue