human
Solve the following python programming problem given the following code:
def _evaluate(self, prediction) : 
    'Helper method to get the precision and recall of 1 sample' 
    def calc_prop_distance(ref, pred) : 
        if (len (ref) == 0) : 
            return 1.0 
diff = len ((set (ref) - set (pred))) 
        return ((len (ref) - diff) / float (len (ref))) 
wordlist = sorted ((set (prediction.keys ()) & set (self.reference.keys ()))) 
    recall_sum = 0.0 
    precis_sum = 0.0 
    for word in wordlist : 
        if (len (word) < 2) : 
            continue 
recall_sum += max ((calc_prop_distance (r, p) for (p, r) in product (prediction [word], self.reference [word]))) 
        precis_sum += max ((calc_prop_distance (p, r) for (p, r) in product (prediction [word], self.reference [word]))) 
precision = (precis_sum / len (wordlist)) 
    recall = (recall_sum / len (wordlist)) 
    f_score = (2.0 / ((1.0 / precision) + (1.0 / recall))) 
    return (precision, recall, prediction, len (wordlist)) 

    
    

    Fix the buggy line: return (precision, recall, prediction, len (wordlist))
assistant
#Here is Python program to fix the buggy line: return (precision, recall, prediction, len (wordlist))
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return (precision, recall, f_score, len (wordlist))