human
Solve the following python programming problem given the following code:
def _sort_metrics(self, metrics) : 
    def sort_by(m) : 
        return (m [0], m [1], m [3]) 
return sorted (metrics, key = self) 

    
    

    Fix the buggy line: return sorted (metrics, key = self)
assistant
#Here is Python code to fix the buggy line: return sorted (metrics, key = self)
.

return sorted (metrics, key = def sort_by()