python - 从列表中获取唯一元组，Python

Question

>>> a= ('one', 'a')
>>> b = ('two', 'b')
>>> c = ('three', 'a')
>>> l = [a, b, c]
>>> l
[('one', 'a'), ('two', 'b'), ('three', 'a')]

我如何才能只检查此列表中具有唯一第二个条目(列？项目？)的元素，然后获取在列表中找到的第一个条目。期望的输出是

>>> l
[('one', 'a'), ('two', 'b')]

Answer 1

使用集合(如果第二项是可散列的):

>>> lis = [('one', 'a'), ('two', 'b'), ('three', 'a')]
>>> seen = set()
>>> [item for item in lis if item[1] not in seen and not seen.add(item[1])]
[('one', 'a'), ('two', 'b')]

上面的代码等价于:

>>> seen = set()
>>> ans = []
for item in lis:
    if item[1] not in seen:
        ans.append(item)
        seen.add(item[1])
...         
>>> ans
[('one', 'a'), ('two', 'b')]