Python Help -- Apply a procedure repeatedly

[boapython]

Hi, I'm trying to write a function that takes in as arguments a procedure with one argument and an integer. The integer represents how many times the procedure will execute on the argument.

def compose(f,g):
    return lambda x: f(g(x))


def repeatedlyApply (p,n):
    i=0
    q=0
    while (i<n):
        q = compose(p,p)
        i=i+2
    return q

This is what I had in mind... I had q = q + compose(p,p) but it tells me it can't add a function and an integer. Which I see. But when I have what's written above, it returns the value of q and not a memory location.

I'm a brand new programmer... Any ideas would be greatly appreciated.

[bartonc]

Hi, I'm trying to write a function that takes in as arguments a procedure with one argument and an integer. The integer represents how many times the procedure will execute on the argument.

def compose(f,g):
    return lambda x: f(g(x))


def repeatedlyApply (p,n):
    i=0
    q=0
    while (i<n):
        q = compose(p,p)
        i=i+2
    return q

This is what I had in mind... I had q = q + compose(p,p) but it tells me it can't add a function and an integer. Which I see. But when I have what's written above, it returns the value of q and not a memory location.

I'm a brand new programmer... Any ideas would be greatly appreciated.

I'm going to look at your code when I get a break. I just wanted to whip off a quick note to welcome you and say "for a beginner you sure got a great handle". Thanks for joining,
Barton

[boapython]

I'm going to look at your code when I get a break. I just wanted to whip off a quick note to welcome you and say "for a beginner you sure got a great handle". Thanks for joining,
Barton

Thanks a lot, Barton!

[bvdet]

Hi, I'm trying to write a function that takes in as arguments a procedure with one argument and an integer. The integer represents how many times the procedure will execute on the argument.

def compose(f,g):
    return lambda x: f(g(x))


def repeatedlyApply (p,n):
    i=0
    q=0
    while (i<n):
        q = compose(p,p)
        i=i+2
    return q

This is what I had in mind... I had q = q + compose(p,p) but it tells me it can't add a function and an integer. Which I see. But when I have what's written above, it returns the value of q and not a memory location.

I'm a brand new programmer... Any ideas would be greatly appreciated.

What type of arguments do you intend to pass to repeatedlyApply ? It appears that one of the arguments, 'p', is another function like 'sqrt'. Function compose returns an anonymous function which must be evaluated in order to return a value. Can you give us some more information so we can better help you?
This all I could come up with:

def compose(f,g):
    return lambda x: f(g(x))

def repeatedlyApply (p, n, v):
    for _ in [num for num in range(n) if num % 2 == 1]:
        z = compose(p,p)
        print z
        v = z(v)
    return v

from math import sqrt

print repeatedlyApply(sqrt, 5, 15823959.67)

"""
>>> <function <lambda> at 0x00E10F30>
<function <lambda> at 0x00DD14F0>
2.81810517827
>>>
"""

[boapython]

Okay, sorry about that... so say if I put in:

repeatedlyApply (lambda x: 2*x,3)("abc")

I should get: 'abcabcabcabcab cabcabcabc'

or repeatedlyApply (lambda x: x+1,10)(100)

should yield 110

The first argument I pass is a function with one argument of its own (In the first case "abc" and in the second "100") and the second is the number of times to repeat the operation on the variable and add to the total.

[bvdet]

Okay, sorry about that... so say if I put in:

repeatedlyApply (lambda x: 2*x,3)("abc")

I should get: 'abcabcabcabcab cabcabcabc'

or repeatedlyApply (lambda x: x+1,10)(100)

should yield 110

The first argument I pass is a function with one argument of its own (In the first case "abc" and in the second "100") and the second is the number of times to repeat the operation on the variable and add to the total.

Something like this?

def repeatedlyApply (f, x, y, n):
    q = 0
    for i in range(n):
        q += f(x,y)
    return q

func = lambda x, y: x**2+y**2-8

print repeatedlyApply(func, 6, 4, 6)

>>> 264

[ghostdog74]

Okay, sorry about that... so say if I put in:

repeatedlyApply (lambda x: 2*x,3)("abc")

I should get: 'abcabcabcabcab cabcabcabc'

or repeatedlyApply (lambda x: x+1,10)(100)

should yield 110

The first argument I pass is a function with one argument of its own (In the first case "abc" and in the second "100") and the second is the number of times to repeat the operation on the variable and add to the total.

you might be better off using map() or list comprehension. just an example only

>>> map(lambda x: 3*x, ["abc"])
['abcabcabc']

[boapython]

Thanks guys! Exactly what I needed, :-)

Hopefully when I get better at this stuff, I can come back here and contribute.

[bartonc]

Thanks guys! Exactly what I needed, :-)

Hopefully when I get better at this stuff, I can come back here and contribute.

Come back any time with questions, too. Keep posting,
Barton

[markus314]

Hi!

I've just found this through google.

You can define:

from functools import partial
from itertools import repeat

def compose(f, g): #  also in the functional module
    def func(*args, **kwargs):
        return f(g(*args, **kwargs))
    return func

mcompose = partial(reduce, compose)
apply_n_times = compose(mcompose, repeat)

Then you get:

>>> def f(x):
...     return 2 * x
>>> apply_n_times(f, 3)("abc")
'abcabcabcabcabcabcabcabc'
>>> apply_n_times(f, 3)(2)
16

[boxfish]

It's great that you could answer this question, but it's really old and was answered already. If you want to answer any fairly recently asked questions, I'm sure your help will be appreciated. Please read the posting guidelines.
Thanks.