Chaining function applications in python

Question

Is there a shortcut in python for applying the same function multiple times to a variable (and its output)?

Something like:

# n times foo(x)

instead of

foo(foo(foo...(foo(x))))...)

John La Rooy · Accepted Answer · 2012-05-16 05:42:19Z

6

for i in range(n):
    x = foo(x)

If you need to preserve x, use a different name

baz = x
for i in range(n):
    baz = foo(baz)

If you are desperate for a shortcut (eg. for codegolf)

reduce(lambda x,y:foo(x),[x]*n)

answered May 16, 2012 at 5:42

John La Rooy

306k54 gold badges378 silver badges513 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

the shortcut is too smart.

jamylak · Accepted Answer · 2012-05-16 05:43:03Z

3

def double(x):
    return x * 2

i = 44
for i in xrange(1,100):
    i = double(i)

Could you mean a simple for loop?

jamylak

134k30 gold badges238 silver badges240 bronze badges

answered May 16, 2012 at 5:42

Jakob Bowyer

34.8k8 gold badges80 silver badges91 bronze badges

Ritesh Kadmawala · Accepted Answer · 2012-05-16 05:51:15Z

1

One of the ways i can think of is creating a generic recursive function to do this

def repeatX(foo, output, count):
      if not count:
         return output
      else:
         return repeatX(foo, foo(output), count -1)

answered May 16, 2012 at 5:51

Ritesh Kadmawala

7531 gold badge10 silver badges17 bronze badges

Unchecked recursion in python is pretty much always a bad idea.