OK my lazywebbers with IPv6 and Python experience, this goes out to you!

I am creating an application right now, with Python of course, and I need to set an environment variable to be always on when a user logs in. I have messed with the os.environ and the os.putenv and what not, but it doesn’t work permanently. This application doesn’t do anything more than a few tests and then sets the environment variable if the tests return true. Is there an easy way to write to ~/.bashrc or ~/.bash_profile to enable the variable, and then later on if the user wants they can disable the variable which would either remove the variable all together or would set it to False?

Another question I have is with IPv6. Is there an easy way to test and see if your network is an IPv6 network or an IPv4 network? Right now I am grepping /var/log/syslog for ‘no IPv6 router present’ and printing the ‘no’. If it is ‘no’ then the network is IPv4, and if it returns 0, then it is an IPv6 network. This is rather hackish I feel, but it does work. Just wondering if there is a better method to do this simple task.

Thanks everyone!