我如何将函数应用n次? [英] how do I apply a function n times?

问题描述

我一直在尝试实现一个将要采用的高阶函数，但并没有取得太大的成功.repeat(f，n)其中，f是另一个函数，n是表示将n应用于变量x的次数的整数值.例如:

I have been trying without much success to implement a higher order function that would take in repeat(f, n) where f is another function and n is the integer value that says how many times n will be applied to a variable x. For example:

def integer(x):

      x + 1

所以我将重复(integer，5)并且我将使用integer(integer(integer(integer(integer(x)

so i would have repeat (integer, 5) and I would have integer(integer(integer(integer(integer(x)

推荐答案

嗯，有一种迭代方法:

def repeat(f, n):
    def new_fn(x):
        for _ in range(n):
            x = f(x)
        return x
    return new_fn

higher_fn = repeat(lambda x: x+3, 5)

higher_fn(2)    # => 17 == (((((2 + 3) + 3) + 3) + 3) + 3)

和组成方法:

def repeat(f, n):
    new_fn_str = "lambda x: {}x{}".format("f(" * n, ")" * n)
    new_fn     = eval(new_fn_str, {"f": f})
    return new_fn

结果完全相同，但可能会更快.

which results in exactly the same thing but may be slightly faster.

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