code: def remember_forever(self, key, callback):
          
          # If the item exists in the cache we will just return this immediately
          # otherwise we will execute the given callback and cache the result
          # of that execution forever.
          val = self.get(key)
          if val is not None:
              return val
  
          val = value(callback)
  
          self.forever(key, val)
  
          return val
docs: Get an item from the cache, or store the default value forever.
  
          :param key: The cache key
          :type key: str
  
          :param callback: The default function
          :type callback: mixed
  
          :rtype: mixed