How to repeat a function n times

Question

I'm trying to write a function in python that is like:

def repeated(f, n):
    ...

where f is a function that takes one argument and n is a positive integer.

For example if I defined square as:

def square(x):
    return x * x

and I called

repeated(square, 2)(3)

this would square 3, 2 times.

Answer 1

That should do it:

 def repeated(f, n):
     def rfun(p):
         return reduce(lambda x, _: f(x), xrange(n), p)
     return rfun

 def square(x):
     print "square(%d)" % x
     return x * x

 print repeated(square, 5)(3)

output:

 square(3)
 square(9)
 square(81)
 square(6561)
 square(43046721)
 1853020188851841

or lambda-less?

def repeated(f, n):
    def rfun(p):
        acc = p
        for _ in xrange(n):
            acc = f(acc)
        return acc
    return rfun

Answer 2

Using reduce and lamba. Build a tuple starting with your parameter, followed by all functions you want to call:

>>> path = "/a/b/c/d/e/f"
>>> reduce(lambda val,func: func(val), (path,) + (os.path.dirname,) * 3)
"/a/b/c"