Question

在Javascript中，我可以使用destructuring从一个衬里的javascript对象中提取所需的属性。例如：

currentUser = {
  "id": 24,
  "name": "John Doe",
  "website": "http://mywebsite.com",
  "description": "I am an actor",
  "email": "example@example.com",
  "gender": "M",
  "phone_number": "+12345678",
  "username": "johndoe",
  "birth_date": "1991-02-23",
  "followers": 46263,
  "following": 345,
  "like": 204,
  "comments": 9
}

let { id, username } = this.currentUser;
console.log(id) // 24
console.log(username) //johndoe

对于Python字典和Python对象，我们在Python中是否有类似的东西？ python对象的Python处理方式示例：

class User:
    def __init__(self, id, name, website, description, email, gender, phone_number, username):
        self.id = id
        self.name = name
        self.website = website
        self.description = description
        self.email = email
        self.gender = gender
        self.phone_number = phone_number
        self.username = username

current_user = User(24, "Jon Doe", "http://mywebsite.com", "I am an actor", "example@example.com", "M", "+12345678", "johndoe")

# This is a pain
id = current_user.id
email = current_user.email
gender = current_user.gender
username = current_user.username

print(id, email, gender, username)

写那4行（如上面的示例中提到的）而不是写一行（如下面提到的）以从对象中获取我需要的值是一个真正的痛点。

(id, email, gender, username) = current_user

Answer 1

您可以按以下方式使用标准库中的operator模块：

from operator import attrgetter
id, email, gender, username = attrgetter('id', 'email', 'gender', 'username')(current_user)
print(id, email, gender, username)

如果您的示例中有类似的格言

currentUser = {
  "id": 24,
  "name": "John Doe",
  "website": "http://mywebsite.com",
  "description": "I am an actor",
  "email": "example@example.com",
  "gender": "M",
  "phone_number": "+12345678",
  "username": "johndoe",
  "birth_date": "1991-02-23",
  "followers": 46263,
  "following": 345,
  "like": 204,
  "comments": 9
}

只需使用itemgetter而不是attrgetter：

from operator import itemgetter
id, email, gender, username = itemgetter('id', 'email', 'gender', 'username')(currentUser)
print(id, email, gender, username)

Answer 2

您可以使用.values()方法解压缩来破坏python字典并提取属性：

 currentUser = {
  "id": 24,
  "name": "John Doe",
  "website": "http://mywebsite.com",
  "description": "I am an actor",
  "email": "example@example.com",
  "gender": "M",
  "phone_number": "+12345678",
  "username": "johndoe",
  "birth_date": "1991-02-23",
  "followers": 46263,
  "following": 345,
  "like": 204,
  "comments": 9
}

id, _, _, _, _, _, _, username, *other = currentUser.values()

print('distructuring:', { 'id': id, 'username': username })

Answer 3

您可以实现__iter__方法来启用拆包：

class User:
  def __init__(self, **data):
    self.__dict__ = data
  def __iter__(self):
    yield from [getattr(self, i) for i in ('id', 'email', 'gender', 'username')]

current_user = User(**currentUser)
id, email, gender, username = current_user
print([id, email, gender, username])

输出：

[24, 'example@example.com', 'M', 'johndoe']

编辑：Python2解决方案：

class User:
  def __init__(self, **data):
    self.__dict__ = data
  def __iter__(self):
    for i in ('id', 'email', 'gender', 'username'):
      yield getattr(self, i)

编辑2：

获取选择属性：

class User:
  def __init__(self, **data):
     self.__dict__ = data
  def __getattr__(self, _vals):
     yield from [getattr(self, i) for i in _vals.split('_')]

current_user = User(**currentUser)
id, email, gender, username = current_user.id_email_gender_username
id, gender = current_user.id_gender

Answer 4

首先不要弄平参数。当您像使用User一样编写8进制函数时，必然会出错，例如以错误的顺序传递参数。

以下哪个会产生您想要的用户？

User(24, "Jon Doe", "http://mywebsite.com", "I am an actor", "example@example.com", "M", "+12345678", "johndoe")
User(24, "Jon Doe", "http://mywebsite.com", "I am an actor", "example@example.com", "+12345678", "M", "johndoe")

不可能知道！如果您的函数采用描述符，则不会出现此问题-

class User:
  def __init__ (self, desc = {}):
    self.desc = desc # whitelist items, if necessary

  def __str__ (self):
    # invent our own "destructuring" syntax
    [ name, age, gender ] = \
      destructure(self.desc, 'name', 'age', 'gender')

    return f"{name} ({gender}) is {age} years old"

# create users with a "descriptor"
u = User({ 'age': 2, 'gender': 'M' })
v = User({ 'gender': 'F', 'age': 3 })
x = User({ 'gender': 'F', 'name': 'Alice', 'age': 4 })

print(u) # None (M) is 2 years old
print(v) # None (F) is 3 years old
print(x) # Alice (F) is 4 years old

我们可以将自己的destructure定义为-

def destructure (d, *keys):
  return [ d[k] if k in d else None for k in keys ]

这仍然可能导致长链，但是顺序取决于调用者，因此它并不像原始问题中的8进制函数那样脆弱-

[ name, age, gender ] = \
  destructure(self.desc, 'name', 'age', 'gender')

# works the same as

[ gender, name, age ] = \
  destructure(self.desc, 'gender', 'name', 'age')

另一种选择是使用关键字参数-

class User:
  def __init__ (self, **desc):
    self.desc = desc # whitelist items, if necessary

  def __str__ (self):
    [ name, age, gender ] = \
      destructure(self.desc, 'name', 'age', 'gender')

    return f"{name} ({gender}) is {age} years old"

# create users with keyword arguments
u = User(age = 2, gender = 'M')
v = User(gender = 'F', age = 3)
x = User(gender = 'F', name = 'Alice', age = 4)

print(u) # None (M) is 2 years old
print(v) # None (F) is 3 years old
print(x) # Alice (F) is 4 years old

Answer 5

在其他答案的基础上，我建议也使用Python的dataclasses并使用__getitem__来获取特定字段：

from dataclasses import astuple, dataclass

@dataclass
class User:
    id: int
    name: str
    website: str
    description: str
    email: str
    gender: str
    phone_number: str
    username: str
    
    def __iter__(self):
        return iter(astuple(self))
    
    def __getitem__(self, keys):
        return iter(getattr(self, k) for k in keys)
        

current_user = User(id=24, name="Jon Doe", website="http://mywebsite.com", description="I am an actor", email="example@example.com", gender="M", phone_number="+12345678", username="johndoe")

# Access fields sequentially:
id, _, email, *_ = current_user
# Access fields out of order:
id, email, gender, username = current_user["id", "email", "gender", "username"]

用Python解构字典和对象

5 个答案: