Test if string ONLY contains given characters

Question

What\'s the easiest way to check if a string only contains certain specified characters in Python? (Without using RegEx or anything, of course)

Specifically, I have

Answer 1

The question is somewhat ambiguous about re-using letters from the base string. Or if there should or should not be repeats, or missing letters allowed. This solution addresses that with a function including a reuse parameter:

from collections import Counter

def anagram_filter(data, base, reuse=True):
    if reuse: # all characters in objects in data are in base, count ignored
        base = set(base)
        return [d for d in data if not set(d).difference(base)]
    r = []
    cb = Counter(base)
    for d in data:
        for k, v in Counter(d).iteritems():
            if (k not in cb.keys()) or (v > cb[k]):
                break
        else:
            r.append(d)
    return r

Usage:

>>> anagram_filter(['aba', 'acba', 'caz'], 'abc')
['aba', 'acba']
>>> anagram_filter(['aba', 'acba', 'caz'], 'abc', False)
[]
>>> anagram_filter(['aba', 'cba', 'caz'], 'abc', False)
['cba']