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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def remember_forever(self, key, callback):
 """ 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 """

        # 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