old_contents: """:class:`BasePreprocessor` define input and ouutput for processors."""
  
  import abc
  import typing
  
  from matchzoo import datapack
  
  
  class BasePreprocessor(metaclass=abc.ABCMeta):
      """:class:`BasePreprocessor` to input handle data."""
  
      @abc.abstractmethod
      def fit(self) -> typing.Callable:
          """
          Fit parameters on input data.
  
          This method is an abstract base method, need to be
          implemented in the child class.
  
          This method is expected to return itself as a callable
          object.
          """
  
      @abc.abstractmethod
      def transform(self) -> datapack.DataPack:
          """
          Transform input data to expected manner.
  
          This method is an abstract base method, need to be
          implemented in the child class.
          """
  
      def fit_transform(self) -> datapack.DataPack:
          """Call fit-transform."""
          return self.fit().transform()
  
new_contents: """:class:`BasePreprocessor` define input and ouutput for processors."""
  
  import abc
  
  from matchzoo import datapack
  
  
  class BasePreprocessor(metaclass=abc.ABCMeta):
      """:class:`BasePreprocessor` to input handle data."""
  
      @abc.abstractmethod
      def fit(self) -> 'BasePreprocessor':
          """
          Fit parameters on input data.
  
          This method is an abstract base method, need to be
          implemented in the child class.
  
          This method is expected to return itself as a callable
          object.
          """
  
      @abc.abstractmethod
      def transform(self) -> datapack.DataPack:
          """
          Transform input data to expected manner.
  
          This method is an abstract base method, need to be
          implemented in the child class.
          """
  
      def fit_transform(self) -> datapack.DataPack:
          """Call fit-transform."""
          return self.fit().transform()
  
subject: adjust fit type hints