code: def chunk(iterable, chunk_size=20):
      
      items = []
      for value in iterable:
          items.append(value)
          if len(items) == chunk_size:
              yield items
              items = []
      if items:
          yield items
docs: chunk an iterable [1,2,3,4,5,6,7,8] -> ([1,2,3], [4,5,6], [7,8])