import re

# how one would normally do it
def contains_foobar_1(s):
    return "foobar" in s.lower()

# how one does it with regex, properly
def contains_foobar_2(s):
    return re.search(r'foobar', s, flags = re.IGNORECASE) is not None

# how one does it with regex
# (trying to squeeze every bit of efficiency outta it)
_foobar_re = re.compile(r'foobar', flags = re.IGNORECASE)
def contains_foobar_3(s):
    return _foobar_re.search(s) is not None