python - 如何从嵌套列表中删除项目

Question

给定一个排序选票列表和一个要淘汰的候选人列表，我需要返回一个新的排序选票列表，其中要淘汰的候选人列表中的所有候选人都已被删除。

这是我到目前为止尝试过的代码

import doctest 

def eliminate_candidate(ballots, to_eliminate):
    '''
    (list, list) -> list

    >>> eliminate_candidate([['NDP', 'LIBERAL'], ['GREEN', 'NDP'], \
    ['NDP', 'BLOC']], ['NDP', 'LIBERAL'])
    [[], ['GREEN'], ['BLOC']]
    >>> eliminate_candidate([], [])
    []
    >>> eliminate_candidate([[]], [])
    [[]]
    '''
    new_list = []

    # Copy ballots onto new list
    for item in ballots:
        new_list.append(item)

    for item in new_list:
        for element in item:
            if element in to_eliminate:
                item.remove(element)

    return new_list

我的第一个 doctest 失败了，而是给我这个输出:

[['LIBERAL'], ['GREEN'], ['BLOC']]

Answer 1

使用 sets 变得非常简单!

ballots = [['NDP', 'LIBERAL'], ['GREEN', 'NDP'], ['NDP', 'BLOC']]
to_eliminate = ['NDP', 'LIBERAL']

result = [list(set(x) - set(to_eliminate)) for x in ballots]
result
[[], ['GREEN'], ['BLOC']]

或者:

result = [list(set(x).difference(to_eliminate)) for x in ballots]
result
[[], ['GREEN'], ['BLOC']]