code: async def rpoplpush(self, src, dst):
          
          value = await self.rpop(src)
  
          if value:
              await self.lpush(dst, value)
              return value
  
          return None
docs: RPOP a value off of the ``src`` list and atomically LPUSH it
          on to the ``dst`` list.  Returns the value.
  
          Cluster impl:
              Call rpop() then send the result into lpush()
  
              Operation is no longer atomic.