Lambda function not working properly

Question

I am trying to write a lambda function to do the same program which I already implemented using a while loop, but I am not able to figure out how to correct my current program using the lambda function. As here, I want to multiply 4 with decreased value of n. For example, 3 should work like 4*3=12 and then 12*2=24, but here it's multiplying 4 always with 3 if n=3. Using a while loop, I wrote this program like below given in foo function. It's not factorial; basically, I want to print this series for different values of n like:

n=1 ans=4,
n=2 ans=8,
n=3 ans=24,
n=4 ans=96,
n=5 ans= 480.

The logic in foo function is generating this output.

foo= lambda n: 4*n**~-n

def foo(n):
  a=4
  i=1
  while i<=n:
      a*=i
      i+=1
  return a
print(foo(7)) #20160

Why not from math import factorial; foo = lambda n: 4 * factorial(n)? Even better, define a function. Named lambda's are against their purpose. — zondo
– zondo, Commented Jun 21, 2016 at 2:12

zondo · Accepted Answer · 2016-06-21 02:31:32Z

4

~ is a unary bitwise operator meaning NOT. ~x is equivalent to -x - 1. Let's break this down:

4*n**~-n == 4*3**~-3 == 4*3**(~-3) == 4*3**2 == 4*(3**2) == 4*9 == 36

What you want is to find 4 * factorial(n). You can import the math module to do that:

from math import factorial

def foo(n):
    return 4 * factorial(n)

This would interpret to:

from math import factorial

foo = lambda n: 4*factorial(n)

The problem with the above approach is that lambdas were created to be nameless. Using a lambda when you want to use it more than once is against their intent. Just stick with the function.

edited Jun 21, 2016 at 2:31

answered Jun 21, 2016 at 2:26

zondo

20.4k8 gold badges50 silver badges89 bronze badges

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

6 Comments

Katie Over a year ago

Thank you, actually my program is not to find factorial. It will generate numbers like as given above in question statement

zondo Over a year ago

Try out my function. It is indeed factorial. You will find that all test cases pass.

Katie Over a year ago

for n=5, your function will generate 120 while my function will generate 480. its just i don't know how to do it using lambda

zondo Over a year ago

My function generates 480. Try it.

zondo Over a year ago

The simple fact is that lambdas cannot do while loops. You need to find a new way.

|

Collectives™ on Stack Overflow

Lambda function not working properly

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related