code: def list_files(self, prefix, flat=False):
      
      layer_path = self.get_path_to_file("")        
      path = os.path.join(layer_path, prefix)
      for blob in self._bucket.list_blobs(prefix=path):
        filename = blob.name.replace(layer_path, '')
        if not flat and filename[-1] != '/':
          yield filename
        elif flat and '/' not in blob.name.replace(path, ''):
          yield filename
docs: List the files in the layer with the given prefix. 
  
      flat means only generate one level of a directory,
      while non-flat means generate all file paths with that 
      prefix.