input: Write a function that takes a list of integers and returns a list of tuples where each tuple contains the index and the square of each number in the original list. If the given list is empty, then return an empty list.
  
  def square_index(nums):
      return [(index, num ** 2) for index, num in enumerate(nums)]
  
  assert square_index([1, 2, 3, 4, 5])==[(0, 1), (1, 4), (2, 9), (3, 16), (4, 25)]
  assert square_index([])==[]
output: def square_index(nums):
      return [(index, num ** 2) for index, num in enumerate(nums)]