如何在 Python 中将类实例的属性存储在空字典中？

Question

我正在制作一个执行基本银行功能的自定义类。

class Account():
    '''
    A class to perform some basic banking functions
    '''
    UserList = {}   #Empty dictionary to store (UID: name) for each new instance
    def __init__(self, name, balance=0.0, uid=None):
        self.name = name    #The name of the account holder
        self.balance = balance #The initial balance
        self.uid = uid  #User ID number chosen by account holder

    @classmethod
    def new_account(cls):
        '''
        New user can specify details of account through this class method via input()
        '''
        return cls(
            input('Name: '),
            int(input('Balance: ')),
            int(input('UID: ')),
        )

    def withdraw(self, amount):
        if amount > self.balance:
            raise RuntimeError('Amount greater than available balance.')
        else:
            self.balance -= amount
            return print("After a withdrawl of {}, {}'s current balance is {}".format(amount, self.name, self.balance)) #printing balance after withdrawl

    def deposit(self, amount):
        self.balance += amount
        return print("After a deposit of {}, {}'s curent balance is {}".format(amount, self.name, self.balance)) # printing balance after deposit

基本上，新用户是通过创建Account() 类的实例来创建的，它接受名称、初始余额和用户 ID。我添加了一个类方法，以便在调用 Account.new_account() 时通过用户输入获取这些数据。我现在要做的是将每个实例（帐户）的用户 ID 和名称存储在一个空字典中。我已经玩了几个小时了，我的想法是这样的 def add_user(self, uid, name): UserList[int(self.uid)] = self.name 插入某处，但我尝试在我的代码中的几个地方实现它，它继续只返回一个空字典。有人可以帮我指出正确的方向。此外，我正在尝试实现的另外两件事是一种防止用户选择相同 UID 的方法，以及一种要求 UID 正好是 5 个数字的方法。我对 Python 比较陌生。谢谢你。

Answer 1

您可以像之前那样将 dict 定义为类变量，但在 __init__ 方法中添加 UID 作为 dict 的键，而不是单独的 add_user 方法，这样您就可以在以下情况下始终验证 UID无论如何都会实例化一个对象：

class Account():
    users = {}
    def __init__(self, name, balance=0.0, uid=None):
        if uid in self.users:
            raise ValueError("UID '%s' already belongs to %s." % (uid, self.users[uid].name))
        if len(uid) != 5 or not uid.isdigit():
            raise ValueError("UID must be a 5-digit number.")
        self.name = name
        self.balance = balance
        self.uid = uid
        self.users[uid] = self

Answer 2

首先注意到您不能“返回打印（...”，删除打印。

你可以这样做

class Account():
'''
A class to perform some basic banking functions
'''
UserList = {}   #Empty dictionary to store (UID: name) for each new instance
def __init__(self, name, balance=0.0, uid=None):
    self.name = name    #The name of the account holder
    self.balance = balance #The initial balance
    self.uid = uid  #User ID number chosen by account holder
    self.add_user(uid, name)

@classmethod
def new_account(cls):
    '''
    New user can specify details of account through this class method via input()
    '''
    return cls(
        input('Name: '),
        int(input('Balance: ')),
        int(input('UID: ')),
    )

def withdraw(self, amount):
    if amount > self.balance:
        raise RuntimeError('Amount greater than available balance.')
    else:
        self.balance -= amount
        return "After a withdrawl of {}, {}'s current balance is {}".format(amount, self.name, self.balance) #printing balance after withdrawl

def deposit(self, amount):
    self.balance += amount
    return "After a deposit of {}, {}'s curent balance is {}".format(amount, self.name, self.balance) # printing balance after deposit

def add_user(self, uid, name):
    self.UserList[int(uid)] = name

a = Account("新用户", 100, 1)

a.add_user(2, "新用户") a.add_user(3, "新用户")

打印（a.UserList）

这将输出 {1: 'new user', 2: 'new user', 3: 'new user'}

Answer 3

从类名中引用静态变量：

class Account():
    user_list = {}

    def __init__(self, uid):
        self.uid = uid
        Account.user_list[uid] = self


a = Account('uid')
print(a.user_list)
# {'uid': <__main__.Account object at 0x1043e7b38>}

对于它的价值，我认为更好的方法是使用 2 个类（为方便起见，我还使用 dataclasses 自动生成一些功能 - 它不会影响核心逻辑）。那么你就完全不用担心静态变量了。

import dataclasses
from typing import Dict

@dataclasses.dataclass
class Account:
    uid: str


@dataclasses.dataclass
class Bank:
    accounts : Dict[str, Account] = dataclasses.field(default_factory=dict)

    def add_account(self, account):
        if account.uid in self.accounts:
            raise ValueError(f'UID : {account.uid} already exists!')
        self.accounts[account.uid] = account


b = Bank()
a1 = Account('a1')
b.add_account(a1)
print(b)
# Bank(accounts={'a1': Account(uid='a1')})