human
Solve the following python programming problem given the following code:
def __call__(cls, * args, **kwargs) : 
    '
        this method will either create an instance (by calling the default implementation)
        or try to retrieve one from the class-wide cache by inferring the pk value from
        `args` and `kwargs`. If instance caching is enabled for this class, the cache is
        populated whenever possible (ie when it is possible to infer the pk value).

        ' 
    def new_instance() : 
        return super (SharedMemoryModelBase, cls).__call__ (* args, ** kwargs) 
instance_key = cls._get_cache_key (args, kwargs) 
    if (instance_key is None) : 
        return new_instance () 
cached_instance = cls.get_cached_instance (instance_key) 
    if (cached_instance is None) : 
        cached_instance = new_instance () 
        cls.cache_instance (cached_instance, new = True) 
return instance_key 

    
    

    Fix the buggy line: return instance_key
assistant
#Here is Python program to fix the buggy line: return instance_key
.

return cached_instance