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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sent_tokenize(text: str, engine: str = "whitespace+newline") -> List[str]: """ This function does not yet automatically recognize when a sentence actually ends. Rather it helps split text where white space and a new line is found. :param str text: the text to be tokenized :param str engine: choose between 'whitespace' or 'whitespace+newline' :return: list of sentences """


    if not text or not isinstance(text, str):
        return []

    sentences = []

    if engine == "whitespace":
        sentences = re.split(r" +", text, re.U)
    else:  # default, use whitespace + newline
        sentences = text.split()

    return sentences