我可以用json.dumps表示my Simple_Dict_Subclass和List_Subclass，但不能用Custom_Dict_Subclass。当json.dumps在List_Subclass上被调用时，它的__iter__方法也被调用，所以我推断json.dumps将调用字典的items方法。items在Simple_Dict_Subclass中被调用，而不是Custom_Dict_Subclass。如何使Custom_Dict_Subclassjson像Simple_Dict_Subclass一样可序列化？

import json
class Custom_Dict_Subclass(dict):
    def __init__(self):
        self.data = {}
    def __setitem__(self, key, value):
        self.data[key] = value
    def __getitem__(self, key):
        return self.data[key]
    def __str__(self):
        return str(self.data)
    def items(self):
        print("'Items' called from Custom_Dict_Subclass")
        yield from self.data.items()
class Simple_Dict_Subclass(dict):
    def __setitem__(self, key, value):
        super().__setitem__(key, value)
    def __getitem__(self, key):
        return super().__getitem__(key)
    def __str__(self):
        return super().__str__()
    def items(self):
        print("'Items' called from Simple_Dict_Subclass")
        yield from super().items()
class List_Subclass(list):
    def __init__(self):
        self.data = []
    def __setitem__(self, index, value):
        self.data[index] = value
    def __getitem__(self, index):
        return self.data[index]
    def __str__(self):
        return str(self.data)
    def __iter__(self):
        yield from self.data
    def append(self, value):
        self.data.append(value)
d = Custom_Dict_Subclass()
d[0] = None
print(d)             # Works
print(json.dumps(d)) # Does't work
d = Simple_Dict_Subclass()
d[0] = None
print(d)             # Works
print(json.dumps(d)) # Works
l = List_Subclass()
l.append(None)
print(l)             # Works
print(json.dumps(l)) # Works

输出量：

{0: None}   # Custom dict string     working
{}          # Custom dict json.dumps not working
{0: None}   # Simple dict string     working
'Items' called from Simple_Dict_Subclass
{"0": null} # Simple dict json.dumps working
[None]      # List string            working
[null]      # List json.dumps        working