human
Solve the following python programming problem given the following code:
def _caching_callback(self, key, callback) : 
    def _inner_cache(result) : 
        self.cache [key] = (result, (datetime.now () + self.ttl)) 
        callback (result) 
return self 

    
    

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

return def _inner_cache(