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pythonfunctionrecursionfunctional-programming
Hanfei Sun
Hanfei Sun

Reputation: 47061

How to construct such a functional-programming tool in Python?

I want a function named times(), in order to make:

times(func,2) equivalent to lambda x:func(func(x))

and times(func,5) equivalent to lambda x:func(func(func(func(func(x)))))

Is there such a tool in Python? What would the code looks like if I want to write it by myself?

Thanks!

Upvotes: 7

Views: 182

Answers (2)

Hanfei Sun
Hanfei Sun

Reputation: 47061

Thanks, Sven

I found a recursive way to do that, but yours looks more pythonic:

def power(func, n):
    def lazy(x, i=n):
        return func(lazy(x, i-1)) if i > 0 else x
    return lazy    

>>> power(lambda x:x*2,3)(9)
72
>>> power(lambda x:x*2,2)(9)
36
>>> power(lambda x:x*2,1)(9)
18
>>> power(lambda x:x*2,0)(9)
9

And a way implemented with decorator:

def powerize(n):
    def wrapped(func):
        def newfunc(*args):
            return power(func,n)(*args)
        return newfunc
    return wrapped

@powerize(3)
def double_3(x):
    return x*2

>>> double_3(8)
64

Upvotes: 5

Sven Marnach
Sven Marnach

Reputation: 601569

I'd suggest to call this power(), since this is actually the nth power of a function. There is no such thing in the standard library, but you can easily implement it yourself:

def power(f, n):
    def wrapped(x):
        for i in range(n):
            x = f(x)
        return x
    return wrapped

Upvotes: 15

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