def split_sentences(tokens):
    """Split sentences (based on tokenised data), returns sentences as a list of lists of tokens, each sentence is a list of tokens"""
    begin = 0
    for i, token in enumerate(tokens):
        if is_end_of_sentence(tokens, i):
            yield tokens[begin:i+1]
            begin = i+1
    if begin <= len(tokens)-1:
        yield tokens[begin:]