Python类在列表（属性）中看不到第二个对象

Question

我想编码电影分类类，它可以找到（基于一些标准），添加和打印电影。你知道吗

这是我的密码：

class Movie:
    def __init__(self,name,director,year,location):
        self.name = name
        self.director = director
        self.year = year
        self.location = location
        self.information = {'name':self.name,'director':self.director,'year':self.year,'location':self.location}

    def get_name(self):
        return self.name

    def get_director(self):
        return self.director

    def get_year(self):
        return self.year

    def get_location(self):
        return self.location 

    def get_information(self):
        return self.information

    def __str__(self):
        return f"Name = {self.name},director = {self.director},year = {self.year},location = {self.location}"

class Classification:
    def __init__(self):
        self.movie_list = []

    def length(self):
        return len(self.movie_list)

    def __getitem__(self,key):
        if isinstance(self.movie_list,slice):
            return self.movie_list[key]

    def add_movie(self,movie):
        self.movie_list.append(movie)              

    def print_movie(self):
        for movie in self.movie_list:
            print(movie)

    def find_movie(self,**kwargs):
        check_list = []
        for movie in self.movie_list:
            for name,value in kwargs.items():
                if movie.get_information()[name] == value:
                    check_list.append(True)
                else:
                    check_list.append(False)     
            if all(item == True for item in check_list):
                print(movie)
        check_list.clear()

这里我有一个类Movie，Classification；Classification只有一个属性，这是电影列表。但我有两个问题：

a = Movie('Matrix','Dan Yefimov','1999','New York')
b = Movie('Legend','Mak Markus','2005','Kiev')
clasif = Classification()
clasif.add_movie(a)
clasif.add_movie(b)
clasif.find_movie(location = 'New York')

1. find_movie()适用于列表中的第一部电影（a）。但是对于第二个，它什么也不打印，即使我输入了正确的搜索参数。

2. 切片不起作用。没有错误信息，只是没有打印任何内容。

你能帮我解决问题吗？你知道吗

另外，我还想听听一些关于改进我的代码的一般性建议。你知道吗

Answer 1

通过删除不必要的方法，我们可以大大缩短代码。我们也可以将__getitem__传递给列表。我还会在定义length方法时使用__len__。你知道吗

class Movie:
    def __init__(self,name,director,year,location):
        self.name = name
        self.director = director
        self.year = year
        self.location = location
    def __str__(self):
        return f"Name = {self.name},director = {self.director},year = {self.year},location = {self.location}"

class Classification:
    def __init__(self):
        self.movie_list = []    
    def __len__(self):  # __len__ lets you do len(classif)
        return len(self.movie_list)    
    def __getitem__(self,key):
        return self.movie_list[key]    
    def add_movie(self,movie):
        self.movie_list.append(movie)                  
    def print_movie(self):
        for movie in self.movie_list:
            print(movie)       
    def find_movie(self,**kwargs):
        for movie in self.movie_list:
            if all(hasattr(movie, k) and getattr(movie, k) == v for k, v in kwargs.items()):
                print(movie)

Answer 2

以下是您的代码版本，代码会稍微少一点：

class Movie:
    ATTRIBUTES = ('name', 'director', 'year', 'location')

    def __init__(self, name, director, year, location):
        self.name = name
        self.director = director
        self.year = year
        self.location = location

    def __str__(self):
        return ', '.join(
            '{} = {}'.format(attr_name, getattr(self, attr_name))
            for attr_name in self.ATTRIBUTES)


class Classification:
    def __init__(self):
        self.movie_list = []

    def __len__(self):
        return len(self.movie_list)

    def __getitem__(self, key):
        return self.movie_list[key]

    def add_movie(self, movie):
        self.movie_list.append(movie)

    def print_movies(self):
        for movie in self.movie_list:
            print(movie)

    def find_movies(self, **kwargs):
        for movie in self.movie_list:
            do_print = True
            for attr_name, attr_value in kwargs.items():
                if attr_name in Movie.ATTRIBUTES:
                    if getattr(movie, attr_name) != attr_value:
                        do_print = False
            if do_print:
                print(movie)

我在Movie中添加了一个名为ATTRIBUTES的类属性；这在Movie.__str__()和Classification.find_movies()中都有使用。建议避免在代码中大量重复属性。你知道吗

在方法Classification.find_movies()中，我先检查它是否是有效的属性，然后再将它与电影实例进行比较。无效参数将被忽略，但您可以更改代码，使无效参数自动导致电影无法打印（所有将被排除）。你知道吗