code: def clean_data(data):
      
      new_data = []
      VALID = 'abcdefghijklmnopqrstuvwxyz123456789"\'?!.,:; '
      for sample in data:
          new_sample = []
          for char in sample[1].lower():  # Just grab the string, not the label
              if char in VALID:
                  new_sample.append(char)
              else:
                  new_sample.append('UNK')
  
          new_data.append(new_sample)
      return new_data
docs: Shift to lower case, replace unknowns with UNK, and listify