Question

I am messing around with the lambda function and I understand what I can do with it in a simple fashion, but when I try something more advanced I am running into errors and I don’t see why.

Here is what I am trying if you can tell me where I am going wrong it would be appricated.

import math

C = lambda n,k: math.factorial(n)/(math.factorial(k))(math.factorial(n-k))

print C(10,5)

I should note that I am running into errors trying to run the code on Codepad. I do not have access to Idle.

Answer 1

Try this:

from math import factorial
from __future__ import division

C = lambda n, k : factorial(n) / factorial(k) * factorial(n-k)

print C(10,5)
> 3628800.0

You were missing a *, and also it’s possible that the division should take in consideration decimals, so the old division operator / won’t do. That’s why I’m importing the new / operator, which performs decimal division.

UPDATE:

Well, after all it seems like it’s Codepad’s fault – it supports Python 2.5.1, and factorial was added in Python 2.6. Just implement your own factorial function and be done with it, or even better start using a real Python interpreter.

def factorial(n):
    fac = 1
    for i in xrange(1, n+1):
        fac *= i
    return fac