Python自定义类实例存入set后仍有重复值，该如何修复代码？

你自定义的Item类的__eq__方法仅执行了属性比较操作，没有返回布尔值，默认返回None（逻辑上等价于False）。而Python的set去重逻辑为：先判断两个对象的__hash__返回值是否相等，若相等再调用__eq__判断是否返回True，两个条件同时满足才会判定为同一对象进行去重，因此你当前的代码即使hash值一致也无法识别重复实例。

1. 修正__eq__方法，返回所有属性的与比较结果，同时补充类型校验避免和非Item实例比较时报错
2. 补充缺失的math库导入（你代码中调用了math.isnan）

import math

class Item():
    __name = ""
    __cost = 0
    __gender = ""
    __prime = ""

    def has_all_properties(self):
        return bool(self.__name and not math.isnan(self.__cost) and self.__gender and self.__prime)
    
    def clean(self):
        return bool(self.__name and self.__cost <=20 and self.__gender == "male" and self.__prime == "yes")
    
    def __init__(self, name, cost, gender, prime):
        self.__name = name
        self.__cost = cost
        self.__gender = gender
        self.__prime = prime
    
    def __eq__(self, other):
        # 先判断比较对象是否为Item实例
        if not isinstance(other, Item):
            return False
        # 返回所有属性的比较结果
        return self.__name == other.__name and self.__cost == other.__cost and self.__gender == other.__gender and self.__prime == other.__prime
   
    def __hash__(self):
        return hash((self.__name, self.__cost, self.__gender, self.__prime))

    def __repr__(self):
        return f"Item({self.__name},{self.__cost},{self.__gender},{self.__prime})"

    def __tuple__(self): 
        return self.__name, self.__cost, self.__gender, self.__prime

# 测试用的示例array
from numpy import nan
array = [['comic', 20.0, 'male', 'yes'], ['paint', 14.0, 'male', 'no'], ['pen', 5.0, 'female', 'yes'], ['phone case', 9.0, 'female', 'no'], ['headphone', 40.0, 'male', 'yes'], [None, 17.0, 'male', 'yes'], ['pencil ', 40.0, 'female', 'yes'], ['coat', nan, 'male', 'yes'], ['underwear', 15.0, 'male', 'yes'], ['shorts', 17.0, 'female', 'no'], ['goggles', 25.0, 'male', 'no'], ['comic', 20.0, 'male', 'yes'], ['watch', 55.0, 'male', 'yes'], ['notebook', 10.0, 'female', 'no'], ['mug', 58.0, 'male', 'no'], ['UNO', 15.0, None, None]]

mylist = {Item(*k) for k in array}
# 此时mylist中仅会保留1个comic对应的Item实例，重复项已被去除
print(mylist)
filtered = filter(Item.has_all_properties, mylist)
clean = filter(Item.clean, filtered)
result = list(clean)
# print(result)

修复后运行代码，原array中两个重复的['comic', 20.0, 'male', 'yes']元素生成的实例会被set正确识别为同一对象，仅保留一份。

内容的提问来源于stack exchange，提问作者zhangruibo101