input: Write a function to take a list of integers and return a list of tuples, where each tuple contains the index and the square of each number in the original list. If the list is empty, return an empty list. 
  assert square_index([1, 2, 3, 4, 5]) == [(0, 1), (1, 4), (2, 9), (3, 16), (4, 25)]
  assert square_index([0, -1, -2, 3]) == [(0, 0), (1, 1), (2, 4), (3, 9)]
  assert square_index([]) == []
  assert square_index([5]) == [(0, 25)]
output: def square_index(lst):
      return [(i, x**2) for i, x in enumerate(lst)]