input: Write a function to calculate the factorial of a given integer. If the integer is less than or equal to 1, the factorial should return 1. Otherwise, it should recursively calculate the factorial by multiplying the number by the factorial of the number minus one.
  
  
  def factorial(num):
      if num <= 1:
          return 1
      else:
          return num * factorial(num - 1)
  
  
  assert factorial(7) == 5040
  assert factorial(0) == 1
  assert factorial(1) == 1
  assert factorial(5) == 120
  assert factorial(3) == 6
output: def factorial(num):
      if num <= 1:
          return 1
      else:
          return num * factorial(num - 1)