extract dictionary words from a strnig

extract_vocab.py

with open('/usr/share/dict/american-english') as vocab_file:
    _vocab = {line.strip() for line in vocab_file}

def _extract_words(string, min_=3):
    ''' Return set of maximal length, non-overlapping dictionary words in `string`. '''
    words = set()
    candidate_len = len(string)
    while candidate_len >= min_:
        for start in range(0, len(string) - candidate_len + 1):
            candidate = string[start:start+candidate_len]
            if candidate in _vocab:
                words.add(candidate)
                string = string[:start] + string[start+candidate_len:]
                candidate_len = len(string) + 1
                break
        candidate_len -= 1
    return words

print('_extract_words("padlock")', _extract_words('padlock'))
print('_extract_words("lockpad")', _extract_words('lockpad'))
print('_extract_words("abarc")', _extract_words('abarc'))