input: Write a function to implement the instruction described in the task. The function should take a list of integers as input and return a list of tuples containing the index and the square of each number in the original list. 
  assert square_index([1, 2, 3, 4, 5])==[(0, 1), (1, 4), (2, 9), (3, 16), (4, 25)]
  assert square_index([0, 1])==[(0, 0), (1, 1)]
  assert square_index([-1, -2, -3])==[(0, 1), (1, 4), (2, 9)]
  assert square_index([])==[]
output: def square_index(lst):
      return [(i, x**2) for i, x in enumerate(lst)]