Python - 类方法返回对象。如何读取对象数据？ [复制]

Question

学习python和作者没有展示打印Class方法输出的部分。作者只是想演示一下我们可以在哪里使用地图功能。

但我正试图弄清楚如何打印它返回的内容。

class User:
  def __init__(self, username, password):
    self.username = username
    self.password = password
  
  @classmethod
  def from_dict(cls, data):
    return cls(data['username'], data['password'])


users = [
  { 'username': 'rolf', 'password': '123'},
  { 'username': 'teclado', 'password': '1234'}
]


user = [User.from_dict(user) for user in users]
print(user)

或将其打印到终端

user = map(User.from_dict, users)
print(user)

它打印一个参考。我想实际查看数据。

[<__main__.User object at 0x7f54b5e02b80>, <__main__.User object at 0x7f54b5e02d00>]
<map object at 0x7f54b5e02d60>

Answer 1

要么：

1. print的属性直接绕过相当无用的默认repr：

   print(user.username, user.password)
   

   或者...

2. 为该类定义一个__repr__，以便它print(user)（或只是在REPL中回显）有一个有用的字符串形式来显示：

    class User:
        # ... rest of class ...
        def __repr__(self):
            return '{0.__class__.__name__}({0.username!r}, {0.password!r})'.format(self)
   

Answer 2

选项 1：在类的元类中实现 str() 或 repr()

这个选项更可取。

class User:
    def __init__(self, username, password):
        self.username = username
        self.password = password

    @classmethod
    def from_dict(cls, data):
        return cls(data['username'], data['password'])

    def __str__(self):
        return f'username : {self.username}, password : {self.password}'

    def __repr__(self):
        return f'User(username={self.username}, password={self.password})'

users = [
    {'username': 'rolf', 'password': '123'},
    {'username': 'teclado', 'password': '1234'}
]

user = [User.from_dict(user) for user in users]
# [username : rolf, password : 123, username : teclado, password : 1234]
print([u for u in user])

选项 2：使用类 __dict__

仅当您无法更改原始类时。

class User:
    def __init__(self, username, password):
        self.username = username
        self.password = password

    @classmethod
    def from_dict(cls, data):
        return cls(data['username'], data['password'])

users = [
    {'username': 'rolf', 'password': '123'},
    {'username': 'teclado', 'password': '1234'}
]

user = [User.from_dict(user) for user in users]
# [{'username': 'rolf', 'password': '123'}, {'username': 'teclado', 'password': '1234'}]
print([u.__dict__ for u in user])