input: Write a function to create a dictionary which contains a data structure in the form of [x:x^2] where x is the key and x^2 is the value. The input is a list of numbers.
  assert square_dict({'numbers': [1, 2, 3, 4, 5]})=={1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
  assert square_dict({'numbers': [0, -1, -2, -3]})=={0: 0, -1: 1, -2: 4, -3: 9}
  assert square_dict({'numbers': []})=={}
  assert square_dict({'numbers': [7]})=={7: 49}
  assert square_dict({'numbers': [-4, -3, -2, -1, 0, 1, 2, 3, 4]})=={-4: 16, -3: 9, -2: 4, -1: 1, 0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
output: def square_dict(data):
      return {x: x**2 for x in data['numbers']}