input: 
  def is_array_even(arr):
      """
      Check whether an array has an even or odd number of elements.
  
      >>> is_array_even([1, 2, 3, 4])
      True
      >>> is_array_even([1, 2, 3])
      False
      """
      if len(arr) % 2 == 0:
          return True
      else:
          return False
  
output:     if len(arr) % 2 == 0:
          return True
      else:
          return False