python怎样能将字典的key和value都变成无重复的呢？

例子：

    >>> process_purchase([('rice', 'mitsuwa'), ('msg', '99ranch'), \
('eggs', 'costco')])
得出{'mitsuwa': ['rice'], '99ranch': ['msg'], 'costco': ['eggs']}
    >>> process_purchase([('milk', 'ralphs'), ('carrot', 'ralphs'), \
('milk', 'ralphs'), ('carrot', 'costco')])
得出{'ralphs': ['milk', 'carrot', 'milk'], 'costco': ['carrot']}

你题目的解答代码如下：

def process_purchase(li):
    dic = {}
    for v,k in li:
        dic.setdefault(k,[]).append(v)
    return dic

print(process_purchase([('rice', 'mitsuwa'), ('msg', '99ranch'),('eggs', 'costco')]))
# 得出{'mitsuwa': ['rice'], '99ranch': ['msg'], 'costco': ['eggs']}
print(process_purchase([('milk', 'ralphs'), ('carrot', 'ralphs'), ('milk', 'ralphs'), ('carrot', 'costco')]))
# 得出{'ralphs': ['milk', 'carrot', 'milk'], 'costco': ['carrot']}

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