ngrams.py

def ngrams(sequence, depth):
    seq = '^' + sequence + '*'
    res = []
    while depth > 0:
        i, j = 0, depth
        while j <= len(seq):
            res.append(seq[i:j])
            i += 1
            j += 1
        depth -= 1
    res.remove('^')
    res.remove('*')
    return res