How to improve my factorial function in python?

Question

I am new to python and I am required to create a factorial function. I have created a function that gives the factorial of a number but I want some help from stackflow community.

Here is my code

a = 5
b = 1
for i in range(1,a+1):
    b = b * i
    print b

And this is my output:

I am getting 120 (factorial value) but I am also getting other values like 1, 2, 6. How can I only print factorial value and not other values.

Answer 1

You can just use the Math library in the Python, Try this following code

import math
math.factorial(5)

Answer : 120

Or, In your Code, you are trying to print the 'b' inside the loop, So your getting prints in every loop time, just put the print b in the out side of the loop

a = 5
b = 1
for i in range(1,a+1):
    b = b * i
print b

Answer 2

Just to show you a different approach:

def fact(n):
    return reduce(lambda accum, element: accum * element, range(1, n+1), 1)

print fact(5)  # prints 120

Answer 3

If you need to write a function then you'll want something more like this:

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)

This calculates the factorial recursively. If you want an iterative function then the following will do it:

def factorial(n):
    res = 1
    for i in range(1, n+1):
        res *= i
    return res

Otherwise, you could just import the math library and use math.factorial(n) if you don't need to create the function yourself.

Answer 4

Factorials are best calculated with a generator function. To retrieve the last item you can use deque.

def factorial(n):
    ct = 1
    factor = 1
    while ct <= n:
        yield factor
        ct = ct+1
        factor = factor * ct
from collections import deque
x = deque(factorial(10), maxlen=1).pop()
x
3628800

Answer 5

Unindent the print statement so that it is only executed after the loop instead of within it, for every step.

a = 5
b = 1
for i in range(1,a+1):
    b = b * i
print b

Answer 6

You can try doing the factorial using reduce from the functools module.

from functools import reduce
def fact(n):
    print(reduce(lambda n, m: n*m, list(range(1, n+1))))
fact(5) # Output: 120