Python 为循环添加了额外的字典键

我正在尝试编写一个python函数，该函数将以电影标题为键的dict和该电影中的演员列表作为值，并返回一个新dict，其中演员作为键，他们在其中出现的电影作为值。这段代码很接近，但每次运行都会返回不同的结果

以下是原始函数调用：

    movies = {"How to Be Single": ["Alison Brie", "Dakota Johnson",
                               "Rebel Wilson"],
              "The Lego Movie": ["Will Arnett", "Elizabeth Banks",
                             "Alison Brie", "Will Ferrell"]}
    print(stars,movies)

代码如下：

def stars(movies):
# create a new dictionary
films_dict= {}
performances_films = []

# for each movie actor, add as key to new_dict
for movie, actors in movies.items():
    for actor in actors:
        if not actor in films_dict.keys():
            #print(actor)
            performances_films = []
            performances_films.append(movie)
            films_dict[actor] = performances_films
        else:
            performances_films.append(movie)
            films_dict[actor] = performances_films

return(films_dict)

以下是输出：

RUN 1
    {'Rebel Wilson': ['How to Be Single'], 'Will Ferrell': ['The Lego 
    Movie'], 
    'Will Arnett': ['The Lego Movie'], 'Elizabeth Banks': ['The Lego Movie', 
    'The Lego Movie'], 'Alison Brie': ['The Lego Movie', 'The Lego Movie'], 
    'Dakota Johnson': ['How to Be Single']}

RUN 2
{'Will Arnett': ['The Lego Movie'], 'Dakota Johnson': ['How to Be Single'], 'Elizabeth Banks': ['The Lego Movie', 'The Lego Movie'], 'Rebel Wilson': ['How to Be Single'], 'Will Ferrell': ['The Lego Movie'], 'Alison Brie': ['The Lego Movie', 'The Lego Movie']}

---

我认为它要么在每次运行时以不同的顺序遍历dict项，要么在一次运行到下一次运行时保存数据。不管怎样，我似乎都无法解决这个问题。

我真的不明白你为什么要把

性能\u电影

列表放在周围。您只需使用先前在

dict

本身中创建的代码即可

以下是我认为有效的方法：

def stars(movies):
    # create a new dictionary
    films_dict= {}

    # for each movie actor, add as key to new_dict
    for movie, actors in movies.items():
        for actor in actors:
            if not actor in films_dict.keys():
                performances_films = []
                performances_films.append(movie)
                films_dict[actor] = performances_films
            else:
                films_dict[actor].append(movie)

    return(films_dict)

印刷品：

{'Alison Brie': ['How to Be Single', 'The Lego Movie'], 'Dakota Johnson': ['How to Be Single'], 'Rebel Wilson': ['How to Be Single'], 'Will Arnett': ['The Lego Movie'], 'Elizabeth Banks': ['The Lego Movie'], 'Will Ferrell': ['The Lego Movie']}

---

代码中的错误是，

列表

实例性能从一个循环迭代持续到下一个循环迭代。这就是为什么（比如）艾莉森·布里（Alison Brie）将乐高电影列了两次——本来应该为另一名演员添加，但之前为艾莉森·布里（Alison Brie）创建的

列表

实例仍然占据了

表演电影

的名称位置。事实上，看起来多个参与者可能共享同一个

列表

实例

如果在访问字典时使用“默认值”概念，可以大大简化代码。这可以通过使用类来完成：

或者我更喜欢的方法是使用普通的dict及其方法：

---

无论哪种方式，您都可以统一对待每一部新电影，而无需明确测试演员先前的

从影记录成员资格

Python字典是无序的，这就是为什么每次运行的输出都会发生变化。如果您想保持词典中项目的顺序一致，您可能需要使用

{'Alison Brie': ['How to Be Single', 'The Lego Movie'], 'Dakota Johnson': ['How to Be Single'], 'Rebel Wilson': ['How to Be Single'], 'Will Arnett': ['The Lego Movie'], 'Elizabeth Banks': ['The Lego Movie'], 'Will Ferrell': ['The Lego Movie']}

import collections
filmography = collections.defaultdict(list)
for movie, actors in movies.items():
    for actor in actors:
        filmography[actor].append(movie)

filmography = {}                     
for movie, actors in movies.items():
    for actor in actors:
        filmography.setdefault(actor, []).append(movie)