groupby大致上可以達成這些事情

[k for k, g in groupby('AAAABBBCCDAABBB')]  #--> A B C D A B
[list(g) for k, g in groupby('AAAABBBCCD')] #--> AAAA BBB CC D

k就是相同連續字串的單個字元，g就會是整串文字

更多groupby詳細說明可以參考這篇，或參考官方文件，這方法不僅可以用在字串，還可以用在很多地方

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但有一個新的問題：g是一個iterator沒有len()可以用，一般使用 len(tuple(g))，把g實體化就可以算長度

另外一種是參考 more-itertools.ilen 的方法，就可以輕鬆算出長度了

def ilen(iterable):
    """Return the number of items in *iterable*.

        >>> ilen(x for x in range(1000000) if x % 3 == 0)
        333334

    This consumes the iterable, so handle with care.

    """
    # This approach was selected because benchmarks showed it's likely the
    # fastest of the known implementations at the time of writing.
    # See GitHub tracker: #236, #230.
    counter = count()
    deque(zip(iterable, counter), maxlen=0)
    return next(counter)