Script from Microsoft. Lists all environment variables on a computer.

 
import win32com.client
strComputer = "."
objWMIService = win32com.client.Dispatch("WbemScripting.SWbemLocator")
objSWbemServices = objWMIService.ConnectServer(strComputer,"root\cimv2")
colItems = objSWbemServices.ExecQuery("Select * from Win32_Environment")
for objItem in colItems:
    print "Caption: ", objItem.Caption
    print "Description: ", objItem.Description
    print "Install Date: ", objItem.InstallDate
    print "Name: ", objItem.Name
    print "Status: ", objItem.Status
    print "System Variable: ", objItem.SystemVariable
    print "User Name: ", objItem.UserName
    print "Variable Value: ", objItem.VariableValue