Calculating factorials with Python

Question

EDIT: I know I can import factorials but I'm doing this as an exercise

Trying to get the factor of a given number with a function in Python.

For example: factorial(4) = 4 * 3 * 2 * 1 = 24

def factorial(x):
    n = x
    while n >= 0:
        x = n * (n - 1)
        n -= 1
    return x

Haha I should have known that was going to be said. I meant to say I'm trying to make my own math functions just as exercises. — Mr.Smithyyy, Feb 21 '15 at 00:10
Factorial is a good candidate for recursion. Have you tried that? — MarkG, Feb 21 '15 at 00:10
If it's an exercise, why come to SO? Doesn't that defeat the purpose? — Trevor, Feb 21 '15 at 00:13
of coarse its just an excersize ... factorial is not something you would ever actually write for anything ... and almost never use for that matter — Joran Beasley, Feb 21 '15 at 00:14
@threed Yes I thought so too but honestly I got so stumped that I wanted to see the right answer. I'm very new to Python so I'm just doing these exercises to try and expand my skills — Mr.Smithyyy, Feb 21 '15 at 00:14
Well, good luck, and good choice; Python is my favorite language! — Trevor, Feb 21 '15 at 00:16
@threed I've only used it for a day and I already want to toss PHP aside! — Mr.Smithyyy, Feb 21 '15 at 00:17

score 4 · Accepted Answer · answered Feb 21 '15 at 00:13

4

try like this: to make your code work

def factorial(x):
    n = 1   # this will store the factorial value
    while x > 0:
        n = n*x
        x -= 1
    return n

you got many advice on comments follow it

answered Feb 21 '15 at 00:13

Hackaholic

17,534
3
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Thank you for using my existing code to make this, makes it much easier to understand. I appreciate everyone else in the comments that put in their answer, very helpful in seeing other ways of doing it. – Mr.Smithyyy Feb 21 '15 at 00:16
1

nice to see u @JoranBeasley – Hackaholic Feb 21 '15 at 00:17

score 1 · Answer 2 · edited May 23 '17 at 10:28

A good way of approaching this would be using recursion where a function calls itself. See Function for Factorial in Python

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

But in your case your return statement actually breaks out of the while loop. So if you pass in 5 you get 20 back which is obviously not 5! (5 factorial).

Instead, try this:

def factorial(x):
   n = 1
   while x > 1:
       n *= x
       x -= 1
   return n

print (factorial(5))

But do have a go at the recursive approach.

If you really want to cheat try:

import math
math.factorial(n)

score 0 · Answer 3 · answered May 25 '16 at 06:20

0

I present an even shorter code for recursive factorial calculation. Not sure if it is faster or slower than other approaches:

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

fac(10)
3628800

answered May 25 '16 at 06:20

Alex

38,938
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406

score 0 · Answer 4 · answered Nov 11 '20 at 04:08

0

def factorial(n):
    total = 1
    for num in range(2,n+1):
        total *= num
    return total

answered Nov 11 '20 at 04:08

Kate Kiatsiri

53
6

better using for loop than while loop – Kate Kiatsiri Nov 11 '20 at 04:08

Calculating factorials with Python

4 Answers4