附加值的类的Python字典分配给所有字典条目[重复]

Question

我有一本字典，其中 ID 作为键，类作为条目。当我尝试附加到一个特定类的变量时，字典中的所有其他类也被附加到。

class Reaction:
    def __init__(self, bkm_id, ec_nums = [], b_ids = [], k_ids = [], m_ids = [], source = ''):
        self.bkm_id = bkm_id
        self.ec_nums = ec_nums
        self.b_ids = b_ids
        self.k_ids = k_ids
        self.m_ids = m_ids
        self.source = source

        self.substrates = []
        self.products = []

    def add_metabolite(self, metabolite, stoichiometry, subs_prod):
        if subs_prod == 'S':
            self.substrates.append(Substrate_Product(metabolite, stoichiometry))
        elif subs_prod == 'P':
            self.products.append(Substrate_Product(metabolite, stoichiometry))   

定义类。然后如果我输入：

rxna = Reaction('a')

rxnb = Reaction('b')

dict = {}

dict['a'] = rxna

dict['b'] = rxnb

dict
Out[14]: 
{'a': <__main__.Reaction instance at 0x102c51fc8>,
 'b': <__main__.Reaction instance at 0x102c62518>}

dict['a'].b_ids.append('BID')

dict['a'].b_ids
Out[16]: ['BID']

dict['b'].b_ids
Out[17]: ['BID']

rxnb.b_ids
Out[18]: ['BID']

而我只想将“BID”附加到 rxna.b_ids。我错过了什么明显的东西吗？

Answer 1

这些列表在类定义上创建一次，因此由所有实例共享。你想要的：

class Reaction:
    def __init__(self, bkm_id, ec_nums=None, b_ids=None, k_ids=None, m_ids=None, source = '')
        self.bkm_id = bkm_id
        self.ec_nums = ec_nums
        self.b_ids = b_ids or []
        self.k_ids = k_ids or []
        self.m_ids = m_ids or []
        self.source = source

        self.substrates = []
        self.products = []

    def add_metabolite(self, metabolite, stoichiometry, subs_prod):
        if subs_prod == 'S':
            self.substrates.append(Substrate_Product(metabolite, stoichiometry))
        elif subs_prod == 'P':
            self.products.append(Substrate_Product(metabolite, stoichiometry)) 

这就是为什么你从不使用可变对象作为参数默认值的原因（好吧，除非你有充分的理由）。