old_contents: class Cube(object):
      pass
  
new_contents: from .cube_array import CubeArray
  from .cube_abc import CubeABC
  
  
  class Cube(CubeABC):
  
      def __init__(self):
          super().__init__()
          self.__data = CubeArray()
  
      def do_step(self, step):
          pass
  
      def do_formula(self, formula):
          for step in formula:
              self.do_step(step)
          return self
  
subject: Create basic Cube class