input: 
  def first_non_repeating_char(lst):
      """ Find the first non-repeating character in a given list.
      >>> first_non_repeating_char([1, 2, 3, 4, 4, 3, 2, 1])
      1
      >>> first_non_repeating_char(['a', 'b', 'c', 'c', 'b'])
      'a'
      """
      dct = {}
      
      for l in lst:
          if l in dct:
              dct[l] += 1
          else:
              dct[l] = 1
              
      for l in lst:
          if dct[l] == 1:
              return l
              
      return None
  
output:     dct = {}
      
      for l in lst:
          if l in dct:
              dct[l] += 1
          else:
              dct[l] = 1
              
      for l in lst:
          if dct[l] == 1:
              return l
              
      return None