code: def process_one(self, item:ItemBase, processor:PreProcessors=None):
          "Apply `processor` or `self.processor` to `item`."
          if processor is not None: self.processor = processor
          self.processor = listify(self.processor)
          for p in self.processor: item = p.process_one(item)
          return itef process_one(self, item:ItemBase, processor:PreProcessors=None):
          "Apply `processor` or `self.processor` to `item`."
          if processor is not None: self.processor = processor
          self.processor = listify(self.processor)
          for p in self.processor: item = p.process_one(item)
          return item
docs: Apply `processor` or `self.processor` to `item`.