What's the most efficient way to find one of several substrings in Python?

Question

I have a list of possible substrings, e.g. [\'cat\', \'fish\', \'dog\']. In practice, the list contains hundreds of entries.

I\'m processing a string,

Answer 1

I just want to point out the time difference between DisplacedAussie's answer and Tom's answer. Both were fast when used once, so you shouldn't have any noticeable wait for either, but when you time them:

import random
import re
import string

words = []
letters_and_digits = "%s%s" % (string.letters, string.digits)
for i in range(2000):
    chars = []
    for j in range(10):
        chars.append(random.choice(letters_and_digits))
    words.append(("%s"*10) % tuple(chars))
search_for = re.compile("|".join(words))
first, middle, last = words[0], words[len(words) / 2], words[-1]
search_string = "%s, %s, %s" % (last, middle, first)

def _search():
    match_obj = search_for.search(search_string)
    # Note, if no match, match_obj is None
    if match_obj is not None:
         return (match_obj.start(), match_obj.group())

def _map():
    search_for = search_for.pattern.split("|")
    found = map(lambda x: (search_string.index(x), x), filter(lambda x: x in search_string, search_for))
    if found:
        return min(found, key=lambda x: x[0])


if __name__ == '__main__':
    from timeit import Timer


    t = Timer("_search(search_for, search_string)", "from __main__ import _search, search_for, search_string")
    print _search(search_for, search_string)
    print t.timeit()

    t = Timer("_map(search_for, search_string)", "from __main__ import _map, search_for, search_string")
    print _map(search_for, search_string)
    print t.timeit()

Outputs:

(0, '841EzpjttV')
14.3660159111
(0, '841EzpjttV')
# I couldn't wait this long

I would go with Tom's answer, for both readability, and speed.