input: Write a function to return a list of tuples containing the index and the square of each number in the given list of integers.
  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([0, -1, -2])==[(0, 0), (1, 1), (2, 4)]
  assert square_index([])==[]
  assert square_index([5])==[(0, 25)]
  assert square_index([-3, 3])==[(0, 9), (1, 9)]
output: def square_index(nums):
      return [(index, num ** 2) for index, num in enumerate(nums)]