input: Write a function to calculate the factorial of a given number. The function should return the factorial of the provided number. If the given number is 0, the function should return 1.
  def factorial(n):
   fact = 1
   for i in range(2,n+1):
    fact = fact * i
   return fact
  assert factorial(7)==5040
  assert factorial(0)==1
output: def factorial(n):
      fact = 1
      for i in range(2, n + 1):
          fact *= i
      return fact