class_docstr: A preprocessor for tf.data.Dataset.
  
  A preprocessor transforms the dataset using `tf.data` operations.
docstr: Fit the preprocessor with the dataset.
  
  # Arguments
      dataset: an instance of `tf.data.Dataset`.
code: def fit(self, dataset):
      """Fit the preprocessor with the dataset.
  
      # Arguments
          dataset: an instance of `tf.data.Dataset`.
      """
      # TODO: may need to change to a streaming way of fit to reduce the
      # number of iterations through the dataset for speed. Need to be
      # decided when we have more use cases for this fit.
      pass
  
file_path: autokeras/autokeras/engine/preprocessor.py
imports: from autokeras.engine import serializable
label_desc: Use image node_id 1 for calling the Preprocessor obj's underlying member method code with example usage: obj.fit(dataset) without return types