Setting global environment vars from Python or Bash

#!/usr/bin/env python

from os import environ, path, name as os_name, getuid
from sys import exit
from fileinput import input


update_environ = lambda: environ.update(dict(env.split('=')
                                        for env in
                                        open('/etc/environment', 'r').readlines()))

if os_name != 'nt' and getuid() != 0:
    print "Rerun {0} as `sudo`".format(__file__)
    exit(1)


def custom_vars(e_vars):
    if not path.isfile('custom_vars.txt'):
        return e_vars
    with open('custom_vars.txt', 'r') as f:
        for line in f.readline():
            var = line.split()
            e_vars[var[0]] = var[1]


def append_environment(e_vars):
    for line in input('/etc/environment', inplace=True):
        var, _, val = line.partition('=')
        nline = '{var}={val}'.format(var=var, val=e_vars.pop(var, val))
        if nline and nline != '=' and nline != '\n' and nline != '=\n':
            print nline  # inplace editing

    if e_vars:
        lines = filter(lambda l: l != '=\n' and nline != '\n',
                       ['{var}={val}\n'.format(var=k, val=e_vars[k])
                        for k in e_vars])
        with open('/etc/environment', 'a') as f:
            f.writelines(lines)


if __name__ == '__main__':
    environment_vars = {'NOM_REPOS': path.join(path.expanduser("~"), 'NOM'),
                        'NOM_API': path.join('/var', 'www')}

    environment_vars = custom_vars(environment_vars)
    append_environment(environment_vars)

I have written a similar script in Bash; with identical functionality:

#!/usr/bin/env bash

sudo sed -i "/^NOM*/d" /etc/environment
for i in `env | grep NOM | cut -f1 -d=`; do
    unset "$i";
done

function set_var()
{
    VAR="$1"
    VAL="$2"

    sudo sed -i "/^$VAR/d" /etc/environment
    printf "$VAR=$VAL\n" | sudo tee -a /etc/environment > /dev/null

    # make the variable available for use in this script and custom_env_vars.sh
    export "$VAR=$VAL"
}

set_var NOM_REPOS "$HOME/NOM"
set_var NOM_API /var/www

if [ -f custom_env_vars.sh ]; then
    . ./custom_env_vars.sh
else
    echo "You can set custom environment variables in 'custom_env_vars.sh'"
fi