How to set windows environment variable from python

Question

I am writing a python program that needs to store a value in a persistent user environment variable. I believe these values are stored in the registry. I have tried something like this using the winreg python module.

key = winreg.OpenKey(winreg.HKEY_CURRENT_USER, 'Environment', access=winreg.KEY_WRITE)
winreg.SetValueEx(key, envVarName, 0, winreg.REG_SZ, envVarValue)
winreg.Close(key)

I can see from using Registry Editor that this value is successfully set. But if I try and read the value from another python script or from a new powershell instance, I don't see the new value until the machine is rebooted.

What else do I need to do to make this value available to other processes without rebooting?

Ricky Chau · Accepted Answer · 2022-02-24 14:59:47Z

1

Looking at this answer gives a possible answer: https://stackoverflow.com/a/61757725/18300067

os.system("SETX {0} {1} /M".format("start", "test"))

answered Feb 24, 2022 at 14:59

Ricky Chau

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cmking Over a year ago

Using setx in a subprocess is how we have been doing it but it is super slow. Like a second or so to set a value. I was really hoping for a better way.

Cow · Accepted Answer · 2022-02-24 15:12:12Z

1

This is how we do it in production on one of Windows servers (code is simplified):

import winreg

regdir = "Environment-test"
keyname = "Name-test"
keyvalue = "Value-test"

def setRegistry(regdir, keyname, keyvalue):
    with winreg.CreateKey(winreg.HKEY_CURRENT_USER, regdir) as _:
        with winreg.OpenKey(winreg.HKEY_CURRENT_USER, regdir, 0, winreg.KEY_WRITE) as writeRegistryDir:
            winreg.SetValueEx(writeRegistryDir, keyname, 0, winreg.REG_SZ, keyvalue)

def getRegistry(regdir, keyname):
    with winreg.OpenKey(winreg.HKEY_CURRENT_USER, regdir) as accessRegistryDir:
        value, _ = winreg.QueryValueEx(accessRegistryDir, keyname)
        return(value)

If I firstly set the value using:

setRegistry(regdir, keyname, keyvalue)

Then check if it's created:

Now I use the getRegistry and open a PS in admin mode to run it:

print(getRegistry(regdir, keyname))

answered Feb 24, 2022 at 15:12

Cow

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3 Comments

cmking Over a year ago

This sets the value in the registry. The part that I am not getting is how to get values that are set in the Environment registry to be read by new processes with out doing a reboot.

Cow Over a year ago

@cmking I did not have to reboot. Worked fine the first time.

cmking Over a year ago

Did it work to read them as environment variables? By using $env:keyName in a new powershell window for example. This definitely did not work for me.

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