input: Write a function to find a pair of numbers from a given list that add up to a given target. Return the pair as a list.
  
  def find_pair(lst, target):
      for i in range(len(lst)):
          if (target - lst[i]) in lst[i+1:]:
              return [lst[i], target-lst[i]]
  
  assert find_pair([1,2,3,4,4,5,6], 8) == [2, 6]
  assert find_pair([1,2,3,4,4,5,6], 7) == [3, 4]
  assert find_pair([1,2,3,4,4,5,6], 11) == [5, 6]
  assert find_pair([1,2,3,4,4,5,6], 100) == None
  assert find_pair([], 8) == None
output: def find_pair(lst, target):
      for i in range(len(lst)):
          if (target - lst[i]) in lst[i+1:]:
              return [lst[i], target-lst[i]]