text: __all__ = ["UnetCallback"]
  
  from icevision.imports import *
  
  
  class UnetCallback(fastai.Callback):
      def before_batch(self):
          assert len(self.xb) == len(self.yb) == 1
  
          self.learn.records = self.yb[0]
          self.learn.yb = (self.xb[0][1],)
          self.learn.xb = (self.xb[0][0],)
  