[ACCEPTED]-How to get environment from a subprocess?-popen

Here's an example of how you can extract 4 environment variables from a batch or cmd 3 file without creating a wrapper script. Enjoy.

from __future__ import print_function
import sys
import subprocess
import itertools

def validate_pair(ob):
    try:
        if not (len(ob) == 2):
            print("Unexpected result:", ob, file=sys.stderr)
            raise ValueError
    except:
        return False
    return True

def consume(iter):
    try:
        while True: next(iter)
    except StopIteration:
        pass

def get_environment_from_batch_command(env_cmd, initial=None):
    """
    Take a command (either a single command or list of arguments)
    and return the environment created after running that command.
    Note that if the command must be a batch file or .cmd file, or the
    changes to the environment will not be captured.

    If initial is supplied, it is used as the initial environment passed
    to the child process.
    """
    if not isinstance(env_cmd, (list, tuple)):
        env_cmd = [env_cmd]
    # construct the command that will alter the environment
    env_cmd = subprocess.list2cmdline(env_cmd)
    # create a tag so we can tell in the output when the proc is done
    tag = 'Done running command'
    # construct a cmd.exe command to do accomplish this
    cmd = 'cmd.exe /s /c "{env_cmd} && echo "{tag}" && set"'.format(**vars())
    # launch the process
    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, env=initial)
    # parse the output sent to stdout
    lines = proc.stdout
    # consume whatever output occurs until the tag is reached
    consume(itertools.takewhile(lambda l: tag not in l, lines))
    # define a way to handle each KEY=VALUE line
    handle_line = lambda l: l.rstrip().split('=',1)
    # parse key/values into pairs
    pairs = map(handle_line, lines)
    # make sure the pairs are valid
    valid_pairs = filter(validate_pair, pairs)
    # construct a dictionary of the pairs
    result = dict(valid_pairs)
    # let the process finish
    proc.communicate()
    return result

So 2 to answer your question, you would create 1 a .py file that does the following:

env = get_environment_from_batch_command('proc1')
subprocess.Popen('proc2', env=env)

As you say, processes don't share the environment 7 - so what you literally ask is not possible, not 6 only in Python, but with any programming 5 language.

What you can do is to put the environment 4 variables in a file, or in a pipe, and either

• have the parent process read them, and pass them to proc2 before proc2 is created, or
• have proc2 read them, and set them locally

The 3 latter would require cooperation from proc2; the 2 former requires that the variables become 1 known before proc2 is started.

Since you're apparently in Windows, you 9 need a Windows answer.

Create a wrapper batch 8 file, eg. "run_program.bat", and run both 7 programs:

@echo off
call proc1.bat
proc2

The script will run and set its 6 environment variables. Both scripts run 5 in the same interpreter (cmd.exe instance), so 4 the variables prog1.bat sets will be set when 3 prog2 is executed.

Not terribly pretty, but 2 it'll work.

(Unix people, you can do the 1 same thing in a bash script: "source file.sh".)

The Python standard module multiprocessing have a Queues system that allow you to 8 pass pickle-able object to be passed through 7 processes. Also processes can exchange messages 6 (a pickled object) using os.pipe. Remember 5 that resources (e.g : database connection) and 4 handle (e.g : file handles) can't be pickled.

You 3 may find this link interesting : Communication between processes with multiprocessing

Also the 2 PyMOTw about multiprocessing worth mentioning 1 : multiprocessing Basics

sorry for my spelling

You can use Process in psutil to get the environment 10 variables for that Process.

If you want to 9 implement it yourself, you can refer to 8 the internal implementation of psutil. It adapts 7 to some operating system.

Currently supported 6 operating systems are:

• AIX
• FreeBSD, OpenBSD, NetBSD
• Linux
• macOS
• Sun Solaris
• Windows

Eg: In Linux platform, you 5 can find one pid 7877 environment variables 4 in file /proc/7877/environ, just open with rt mode to read it.

Of 3 course the best way to do this is to:

import os
from typing import Dict
from psutil import Process

process = Process(pid=os.getpid())
process_env: Dict = process.environ()

print(process_env)

You 2 can find other platform implementation in 1 source code

Hope I can help you.

Two things spring to mind: (1) make the 9 processes share the same environment, by 8 combining them somehow into the same process, or 7 (2) have the first process produce output 6 that contains the relevant environment variables, that 5 way Python can read it and construct the 4 environment for the second process. I think 3 (though I'm not 100% sure) that there isn't 2 any way to get the environment from a subprocess 1 as you're hoping to do.