在Python中解构dicts和对象

Question

在Javascript中，我可以使用destructuring从一个Javascript对象中提取我想要的属性。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 dict和Python对象，我们在Python中有类似的东西吗？Python对象的Python方法示例：

^{pr2}$

编写这4行代码（如上面的示例所述）与编写一行代码（如下所述）从一个对象中获取所需的值是一个真正的痛点。在

(id, email, gender, username) = current_user

Answer 1

首先，不要把争论搞得平淡无奇。当您像使用User编写8元函数时，您必然会犯错误，例如以错误的顺序传递参数。在

你打算让用户产生以下哪一个？在

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

不可能知道！如果函数使用描述符，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-

^{pr2}$

这仍然可能导致长链，但顺序取决于调用方，因此它不像原问题中的8元函数那样脆弱-

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

# works the same as

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

---

参数是另一个使用关键字-

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 2

您可以实现__iter__方法来启用解包：

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：

^{pr2}$

编辑：Python溶液：

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