old_contents: import dis
  from collections import deque
  
  
  class PythonVM:
      def __init__(self):
          self._stack = deque()
          self._globals = {}
          self._locals = {}
  
      def push(self, value):
          self._stack.pushleft(value)
  
      def pop(self):
          return self._stack.popleft()
  
      def eval(self, bytecode):
          insts = dis.get_instructions(bytecode)
          for inst in insts:
              opcode = inst.opcode
              if opcode == 'NOP':
                  pass
              # General instructions
              elif opcode == 'POP_TOP':
                  self.pop()
              elif opcode == 'ROT_TWO':
                  a = self.pop()
                  b = self.pop()
                  self.push(a)
                  self.push(b)
              elif opcode == 'ROT_THREE':
                  a = self.pop()
                  b = self.pop()
                  c = self.pop()
                  self.push(a)
                  self.push(b)
                  self.push(c)
              elif opcode == 'DUP_TOP':
                  a = self.pop()
                  self.push(a)
                  self.push(a)
              elif opcode == 'DUP_TOP_TWO':
                  a = self.pop()
                  b = self.pop()
                  self.push(b)
                  self.push(a)
                  self.push(b)
                  self.push(a)
  
new_contents: import dis
  from collections import deque
  
  
  class PythonVM:
      def __init__(self):
          self._stack = deque()
          self._globals = {}
          self._locals = {}
  
      def push(self, value):
          self._stack.pushleft(value)
  
      def pop(self):
          return self._stack.popleft()
  
      def eval(self, bytecode):
          insts = dis.get_instructions(bytecode)
          for inst in insts:
              opcode = inst.opcode
              if opcode == 'NOP':
                  pass
              # General instructions
              elif opcode == 'POP_TOP':
                  self.pop()
              elif opcode == 'ROT_TWO':
                  a = self.pop()
                  b = self.pop()
                  self.push(a)
                  self.push(b)
              elif opcode == 'ROT_THREE':
                  a = self.pop()
                  b = self.pop()
                  c = self.pop()
                  self.push(a)
                  self.push(b)
                  self.push(c)
              elif opcode == 'DUP_TOP':
                  a = self.pop()
                  self.push(a)
                  self.push(a)
              elif opcode == 'DUP_TOP_TWO':
                  a = self.pop()
                  b = self.pop()
                  self.push(b)
                  self.push(a)
                  self.push(b)
                  self.push(a)
              # Not implemented operator
              else:
                  raise NotImplementedError(
                      'the opcode `{}` is not implemented.'.format(opcode)
                  )
  
subject: raise NotImplementedError when encountering unimplemented operator