input: Write a python function to check if a number is present in a list.
  assert is_present([1, 2, 3, 4, 5], 3) == True
  assert is_present([1, 2, 3, 4, 5], 6) == False
  assert is_present([10, 20, 30, 40, 50], 50) == True
  assert is_present([], 1) == False
output: def is_present(lst, num):
      return num in lst