factorial of a number using function and without using function in Python

factorial is the product of all the positive integers less than or equal to input number.
!n is also denoted as factorial of a number .

import math
print(math.factorial(4))    # 24

factorial of 4 is 24.

import math
print(math.factorial(12))    # 479001600

Factorial of a number without using the factorial() function

n=12
factorial=1
for i in range (1,n+1):
    factorial=factorial * i
print(factorial)

Output is here

479001600

Recursive Factorial Method

You can also calculate factorial using recursion:

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)
print(factorial(5))

Factorial of 0 is defined as 1:

print(math.factorial(0))

For negative inputs, raise an error. More on try-except

try:
    print(math.factorial(-3))
except ValueError as e:
    print(e)

factorial() not defined for negative values

Find the factorial of an input number. check the number before using factorial() method.
Check your answer without importing math module.

import math
x=input("Enter the number : ")
if x.isdigit():
  print(math.factorial(int(x)))
else:
  print(" Enter correct number ")