Check if multiple strings exist in another string

You can use any:

a_string = "A string is more than its parts!"
matches = ["more", "wholesome", "milk"]

if any(x in a_string for x in matches):

Similarly to check if all the strings from the list are found, use all instead of any.

any() is by far the best approach if all you want is True or False, but if you want to know specifically which string/strings match, you can use a couple things.

If you want the first match (with False as a default):

match = next((x for x in a if x in a_string), False)

If you want to get all matches (including duplicates):

matches = [x for x in a if x in a_string]

If you want to get all non-duplicate matches (disregarding order):

matches = {x for x in a if x in a_string}

If you want to get all non-duplicate matches in the right order:

matches = []
for x in a:
    if x in a_string and x not in matches:
        matches.append(x)

You should be careful if the strings in a or str gets longer. The straightforward solutions take O(S*(A^2)), where S is the length of str and A is the sum of the lenghts of all strings in a. For a faster solution, look at Aho-Corasick algorithm for string matching, which runs in linear time O(S+A).

Just to add some diversity with regex:

import re

if any(re.findall(r'a|b|c', str, re.IGNORECASE)):
    print 'possible matches thanks to regex'
else:
    print 'no matches'

or if your list is too long - any(re.findall(r'|'.join(a), str, re.IGNORECASE))