input: Write a python function to generate a dictionary with numbers as keys and their squares as values.
  assert num_squares() == {1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81, 10: 100}
  assert isinstance(num_squares(), dict)
  assert len(num_squares()) == 10
output: def num_squares():
      return {i: i ** 2 for i in range(1, 11)}