組み込み関数 reduce

次に、組み込み関数 reduce のヘルプ情報を確認します。

>>> help(reduce)

Help on built-in function reduce in module __builtin__:
reduce(...)

    reduce(function, sequence[, initial]) -> value

    

    Apply a function of two arguments cumulatively to the items of a sequence,

    from left to right, so as to reduce the sequence to a single value.

    For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates

    ((((1+2)+3)+4)+5).  If initial is present, it is placed before the items

    of the sequence in the calculation, and serves as a default when the

    sequence is empty.

これを見て、２つまたは３つの引数を与えると、値が得られるのが分かります。実際に、その動作を確認してみましょう。