factorial.py

#Not using float because the we're multiplying not dividng, in multiplying, the end result will always be a whole number.
def factorial(number):
	return 1 if number < 2 else number * factorial(number-1) 
#Used number < 2 instead of number == 1 or number == 0, It's shorter.
try:
	number = int(input("Enter A Number: ")) #Converting To Int cause we can find factorial
	#of only integer and not decimal values .. 
except ValueError:
	#If the user types some other type of data, for example
	#He enters string, we obviously can't find the factorial of string, 
	print("Please Enter A Valid Input.")
	exit() 
factorial(number)