input: 
  def find_index(arr, x):
      """ Find the index of a given value in an array. If the value is not present, return -1.
      >>> find_index(arr=[2, 5, 9, 15], x=5)
      1
      >>> find_index(arr=[2, 5, 9, 15], x=10)
      -1
      """
      for i in range(len(arr)):
          if arr[i] == x:
              return i
      return -1
  
  print(find_index(arr, x))
  
output:     for i in range(len(arr)):
          if arr[i] == x:
              return i
      return -1