input: Write a function to create a dictionary from a list of numbers where each key is a number from the list and its corresponding value is the square of that number. If the input list is empty, the function should return an empty dictionary.
  
  assert square_dictionary([1, 2, 3, 4, 5])=={1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
  assert square_dictionary([5, 3, 7, 1])=={5: 25, 3: 9, 7: 49, 1: 1}
  assert square_dictionary([-2, -1, 0, 1, 2])=={-2: 4, -1: 1, 0: 0, 1: 1, 2: 4}
  assert square_dictionary([])=={}
output: def square_dictionary(numbers):
      return {num: num**2 for num in numbers}