What is the best way for checking if the user of a script has root-like privileges?

os.geteuid gets the effective user id, which is exactly what you want, so I can't think of any better way to perform such a check. The one bit that's uncertain is that "root-like' in the title: your code checks for exactly root, no "like" about it, and indeed I wouldn't know what "root-like but not root" would mean -- so, if you mean something different than "exactly root", perhaps you can clarify, thanks!

Under the "Easier to Ask Forgiveness than Permission" principle:

try:
    os.rename('/etc/foo', '/etc/bar')
except IOError as e:
    if (e[0] == errno.EPERM):
       sys.exit("You need root permissions to do this, laterz!")

If you are concerned about the non-portability of os.geteuid() you probably shouldn't be mucking with /etc anyway.

You can prompt the user for sudo access:

import os, subprocess

def prompt_sudo():
    ret = 0
    if os.geteuid() != 0:
        msg = "[sudo] password for %u:"
        ret = subprocess.check_call("sudo -v -p '%s'" % msg, shell=True)
    return ret

if prompt_sudo() != 0:
    # the user wasn't authenticated as a sudoer, exit?

The sudo -v switch update the user's cached credentials (see man sudo).