การใช้ doctest

def sum_counters(counters):
    """Aggregate collections.Counter objects by summing counts

    :param counters: list/tuple of counters to sum
    :return: aggregated counters with counts summed

    >>> d1 = text_analyzer.Document('1 2 fizz 4 buzz fizz 7 8')
    >>> d2 = text_analyzer.Document('fizz buzz 11 fizz 13 14')
    >>> ____([d1.word_counts, d2.word_counts])
    ____
    """
    return sum(counters, Counter())

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