How to store environment variables

Question

To set an environment variable using Windows Command Processor ( cmd) :

SET MY_VARIABLE=c:\path\to\filename.txt

MY_VARIABLE now can be accessed by Python application started by same cmd window:

import os
variable = os.getenv('MY_VARIABLE') 

I wonder if there is a way to set an environment variable from inside of Python so it becomes available to other processes running on the same machine? To set a new environment variable:

os.environ['NEW_VARIABLE'] = 'NEW VALUE'

But this NEW_VARIABLE is lost as soon Python process and exited.

Answer 1

You can store environment variables persistently in the Windows registry. Variables can be stored for the current user, or for the system:

Code to persistently set an environment variable on Windows:

import win32con
import win32gui
try:
    import _winreg as winreg
except ImportError:
    # this has been renamed in python 3
    import winreg

def set_environment_variable(variable, value, user_env=True):
    if user_env:
        # This is for the user's environment variables
        reg_key = winreg.OpenKey(
            winreg.HKEY_CURRENT_USER,
            'Environment', 0, winreg.KEY_SET_VALUE)
    else:
        # This is for the system environment variables
        reg_key = winreg.OpenKey(
            winreg.HKEY_LOCAL_MACHINE,
            r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment',
            0, winreg.KEY_SET_VALUE)

    if '%' in value:
        var_type = winreg.REG_EXPAND_SZ
    else:
        var_type = winreg.REG_SZ
    with reg_key:
        winreg.SetValueEx(reg_key, variable, 0, var_type, value)

    # notify about environment change    
    win32gui.SendMessageTimeout(
        win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE, 0, 
        'Environment', win32con.SMTO_ABORTIFHUNG, 1000)

Test code to invoke above:

set_environment_variable('NEW_VARIABLE', 'NEW VALUE')