gistfile1.py

#!/usr/bin/env python
import timeit

params = {
    'domain': 'example.com',
    'host': 'www.example.com:8000'
}

string_test = """\
import string
domain = '%(domain)s'
host = '%(host)s'
position = string.find(host, '.%%s:' %% domain)

if position > -1:
    subdomain = host[:position]
""" % params

regex_test = """\
import re
domain = '%(domain)s'
host = '%(host)s'
pattern = r'^(?:(?P<subdomain>.*?)\.)?%%s(?::.*)?$' %% re.escape(domain)
matches = re.match(pattern, host)

if matches:
    subdomain = matches.group('subdomain')
""" % params

print "Testing:\n", string_test
string_timer = timeit.Timer(string_test)
print string_timer.timeit()

print "Testing:\n", regex_test
regex_time = timeit.Timer(regex_test)
print regex_time.timeit()