如何为复杂对象编写自定义JSON解码器?

时间:2018-02-26 15:35:04

标签: json python-3.x serialization decoder

就像标题所说的那样,我试图为我已定义的类包含其他类别I类所定义的对象的对象编写自定义解码器。 "外部" class是一个Edge,定义如下:

class Edge:
    def __init__(self, actor, movie):
        self.actor = actor
        self.movie = movie

    def __eq__(self, other):
        if (self.movie == other.movie) & (self.actor == other.actor):
            return True
        else:
            return False

    def __str__(self):
        print("Actor: ", self.actor, " Movie: ", self.movie)

    def get_actor(self):
        return self.actor

    def get_movie(self):
        return self.movie

使用"内部"类actor和电影定义如下:

class Movie:
    def __init__(self, title, gross, soup, year):
        self.title = title
        self.gross = gross
        self.soup = soup
        self.year = year

    def __eq__(self, other):
        if self.title == other.title:
            return True
        else:
            return False

    def __repr__(self):
        return self.title

    def __str__(self):
        return self.title

    def get_gross(self):
        return self.gross

    def get_soup(self):
        return self.soup

    def get_title(self):
        return self.title

    def get_year(self):
        return self.year

class Actor:
    def __init__(self, name, age, soup):
        self.name = name
        self.age = age
        self.soup = soup

    def __eq__(self, other):
        if self.name == other.name:
            return True
        else:
            return False

    def __repr__(self):
        return self.name

    def __str__(self):
        return self.name

    def get_age(self):
        return self.age

    def get_name(self):
        return self.name

    def get_soup(self):
        return self.soup

(汤只是该电影/演员维基百科页面的美丽对象,可以忽略不计)。 我也为边缘类编写了一个客户编码器:

class EdgeEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, Edge):
            return {
                    "Actor": {
                             "Name": o.get_actor().get_name(),
                             "Age": o.get_actor().get_age()
                             },
                    "Movie": {
                             "Title": o.get_movie().get_title(),
                             "Gross": o.get_movie().get_gross(),
                             "Year": o.get_movie().get_year()
                             }
                    }
        return json.JSONEncoder.default(self, o)

我已经测试过,它正确地将边列表序列化为JSON文件。现在我的问题出现在尝试编写边缘解码器时。我已经使用github页面here作为参考,但我的编码器偏离了他,我想知道是否需要更改它。我是否需要在其JSON序列化中将对象的类型显式编码为其自己的键值对,或者是否有某种方法可以获取" Actor"和"电影"键的边缘序列化?同样,有没有办法抓住" Name"。 " Age"等,这样我可以重建Actor / Movie对象,然后使用它们重建边缘?有没有更好的方法来编码我的对象?我也尝试过this教程,但是我发现对象的使用会让编码器感到困惑,而且我不确定如何将该方法扩展到包含自定义对象的自定义对象。

2 个答案:

答案 0 :(得分:0)

您引用的编码器/解码器示例(here)可以轻松扩展,以允许JSON输入/输出中使用不同类型的对象。

但是,如果您只希望一个简单的解码器与您的编码器匹配(仅将Edge对象编码在JSON文件中),请使用以下解码器:

class EdgeDecoder(json.JSONDecoder):
    def __init__(self, *args, **kwargs):
        json.JSONDecoder.__init__(self, object_hook=self.object_hook, *args, **kwargs)
    def object_hook(self, dct):
        if 'Actor' in dct:
            actor = Actor(dct['Actor']['Name'], dct['Actor']['Age'], '')
            movie = Movie(dct['Movie']['Title'], dct['Movie']['Gross'], '', dct['Movie']['Year'])
            return Edge(actor, movie)
        return dct

使用问题中的代码定义类MovieActorEdgeEdgeEncoder,以下代码将输出测试文件,然后将其读回在:

filename='test.json'
movie = Movie('Python', 'many dollars', '', '2000')
actor = Actor('Casper Van Dien', 49, '')
edge = Edge(actor, movie)
with open(filename, 'w') as jsonfile:
    json.dump(edge, jsonfile, cls=EdgeEncoder)
with open(filename, 'r') as jsonfile:
    edge1 = json.load(jsonfile, cls=EdgeDecoder)
assert edge1 == edge

答案 1 :(得分:-1)

无需使用JSONEncoderJSONDecoder即可解决此问题。

  • 向每个类添加to_dict()方法(负责从python objectJSON dict的转换)
  • 如果您的对象构造函数之一期望使用bool, str, int, and float以外的参数类型,请检查传递的参数是否为dict类型,如果是这种情况,则必须自己构造该对象(请参见{{ 1}})

简化了您的示例:

Edge

返回:

class Edge:
    def __init__(self, actor, movie):
        if type(actor) is Actor:
            self.actor = actor
        else: # type == dict
            self.actor = Actor(**actor)
        if type(movie) is Movie:
            self.movie = movie
        else: # type == dict
            self.movie = Movie(**movie)

    def __eq__(self, other):
        return (self.movie == other.movie) & (self.actor == other.actor)

    def __str__(self):
        return "".join(["Actor: ", str(self.actor), " /// Movie: ", str(self.movie)])

    def to_dict(self):
        return {"actor": self.actor.to_dict(), "movie": self.movie.to_dict()}

class Movie:
    def __init__(self, title, gross, soup, year):
        self.title = title
        self.gross = gross
        self.soup = soup
        self.year = year

    def __eq__(self, other):
        return self.title == other.title

    def __str__(self):
        return self.title

    def to_dict(self):
        return {"title": self.title, "gross": self.gross, "soup": self.soup, "year": self.year}

class Actor:
    def __init__(self, name, age, soup):
        self.name = name
        self.age = age
        self.soup = soup

    def __eq__(self, other):
        return self.name == other.name

    def __str__(self):
        return self.name

    def to_dict(self):
        return {"name": self.name, "age": self.age, "soup": self.soup}


if __name__ == '__main__':
    edge_obj = Edge(Actor("Pierfrancesco Favino", 50, "id0"), Movie("Suburra", 10, "id1", 2015))
    edge_dict = edge_obj.to_dict()
    edge_obj_new = Edge(**edge_dict)

    print("manual edge\t\t", edge_obj)
    print("edge to json\t", edge_dict)
    print("auto edge\t\t", edge_obj_new)
    print("edges equal?\t", edge_obj == edge_obj_new)

您会看到两个manual edge Actor: Pierfrancesco Favino /// Movie: Suburra edge to json {'actor': {'name': 'Pierfrancesco Favino', 'age': 50, 'soup': 'id0'}, 'movie': {'title': 'Suburra', 'gross': 10, 'soup': 'id1', 'year': 2015}} auto edge Actor: Pierfrancesco Favino /// Movie: Suburra edges equal? True 对象相等,第二行以Edge表示形式将Edge输出为dict