啃书-- 流畅的python 第五章 数据类构建器

from collections import namedtuple
coordinate = namedtuple('cordinate','lat lon')  
moscow = coordinate(12.345,16.789)
moscow_new = coordinate(12.345,16.789)
print(moscow == moscow_new) #可以直接比较两个namedtuple instance 是否相等， 只用class 构建的类比较的是两个instance 的id而不是值；

City = namedtuple('City','name country population coordinates')
tokyo = city('Tokyo', 'JP', 36.933, (35.689722, 139.691667))  #构建方法1
print(tokyo)

#构建方法2
nxt = coordinate(33.4565,84.572)
nxt_data = ('shanghai','CH',100,nxt)
shanghai = City._make(nxt_data)
print(shanghai)

# 构建字典
print(shanghai._asdict())

#构建json
import json
json.dumps(shanghai._asdict())

#访问字段
print(city._fields) 
print(shanghai.coordinates)
print(shanghai[-1])

# 设置字段默认值
Point = namedtuple('Point','x y z',defaults=[0,1,2])
a = Point()
b = Point(1)
c = Point(1,2)
print(a,b,c)

True
city(name='Tokyo', country='JP', population=36.933, coordinates=(35.689722, 139.691667))
City(name='shanghai', country='CH', population=100, coordinates=cordinate(lat=33.4565, lon=84.572))
{'name': 'shanghai', 'country': 'CH', 'population': 100, 'coordinates': cordinate(lat=33.4565, lon=84.572)}
('name', 'country', 'population', 'coordinates')
cordinate(lat=33.4565, lon=84.572)
cordinate(lat=33.4565, lon=84.572)
Point(x=0, y=1, z=2) Point(x=1, y=1, z=2) Point(x=1, y=2, z=2)

from typing import NamedTuple
class Point(NamedTuple):
    x:float
    y:float
    def __str__(self):
        if self.x>0 and self.y>0:
            return 'First quadrant'
        elif self.x<0 and self.y>0:
             return 'Second quadrant'
a = Point(8.8,9.0)
print(a)

First quadrant

from dataclasses import dataclass
@dataclass
class point: 
    x:float = 0.0 # 1)提供类型+默认值
    y:float = 0.0 
    def __str__(self):
        if self.x>0 and self.y>0:
            return f'{self.x},{self.y} First quadrant'
        elif self.x<0 and self.y>0:
             return f'{self.x},{self.y} Second quadrant'
        elif self.x == 0.0 and self.y == 0.0:
            return  f'{self.x},{self.y}'
    
pointA = point()
print(pointA)
        

0.0,0.0

from dataclasses import dataclass,field
@dataclass
class ClubMember:
    name:str 
    guests:list = field(default_factory=list) # 2.类属性用作实例属性， 用field 注册 list ， 不能直接写成guests:list =[]
                                              # 每个实例都会有各自的list，而不是所有实例共享一个list
    visitors:list[str] = field(default_factory=list) # 3. 说明list的类型 是str
    athlete:bool =field(default=False,repr=False) 

@dataclass
class HackerClubMember(ClubMember):
    all_handles = set() #类属性 , 所有实例共享
    handle:str = ''     #实例字段
    def __post_init__(self):
        cls = self.__class__  #获取实例所属的类
        if self.handle == '': 
            self.handle = self.name.split()[0]  #如果是空字符串，则设置为name 的第一部分
        if self.handle in cls.all_handles: #如果self.handle 在cls.handle 中
            raise ValueError(f'handle {self.handle} already exists')
        cls.all_handles.add(self.handle) # 把新的handle 添加到cls.all_handles 中
mem1 = HackerClubMember('li haw')
print(mem1)
#mem2 = HackerClubMember('li ai') # raise error , 'li' already exists
mem2 =  HackerClubMember('li ai',handle='liu') 

HackerClubMember(name='li haw', guests=[], visitors=[], handle='li')

from dataclasses import dataclass
from typing import ClassVar  #从typing 中引入ClassVar
 
@dataclass
class Company:
    name:ClassVar[str] = 'tengxun'
    mem:ClassVar[list[str]] = []  #mem ： 类属性，是str-list ，初始值为空list
    def add_mem(self,mem_name):
        cls = self.__class__  #获取当前实例的类
        cls.mem.append(mem_name) #类属性增加内容
Company1 = Company()
Company1.add_mem(mem_name = 'ma')
for item in iter('zhang wang li zhao'.split()):
    Company1.add_mem(item)
print(Company1.mem)

['ma', 'zhang', 'wang', 'li', 'zhao']

from dataclasses import dataclass,InitVar
from typing import ClassVar,Tuple

database = ('TechNova Solutions','BlueSky Innovations','Quantum Dynamics','Pinnacle Enterprises')
@dataclass
class company:
    name:str = None #实例属性
    database:InitVar[tuple[str]] = None  
    mem_num:ClassVar[int] = 0 #类属性
    # def __post_init__(self):             error ： 
    #     cls = self.__class__
    #     if self.name is None and cls.database is not None:
    #         self.name = cls.database[0]   error ： database 不是类属性，访问不到
    def __post_init__(self,database):
        cls = self.__class__
        if self.name is None and database is not None:
            self.name = database[0]
            

company1 = company(database=database)
print(company1)
            

company(name='TechNova Solutions')

import typing
class City(typing.NamedTuple):
    continet:str
    name:str
    country:str
cities = [
    City('Asia', 'Tokyo', 'JP'),
    City('Asia', 'Delhi', 'IN'),
    City('North America', 'Mexico City', 'MX'),
    City('North America', 'New York', 'US'),
    City('South America', 'São Paulo', 'BR'),
]
result_Asia = []
result_America = []
#关键字匹配
for city in cities:
    match city:
        case City(continet = 'Asia'): # 注意不是 City(continet == 'Asia') ，
                                      # city 匹配  City(continet = 'Asia')  ，continet的属性值='Asia'
            result_Asia.append(city)
        case City(continet ='North America' ,country ='cc'): #匹配2个属性
            result_America.append(city)
    
print(result_Asia)
print(result_America)       

#位置类匹配
result_pos = []
for city in cities:
    match city:
        case City('Asia',_,Country):
            result_pos.append(city)
            print(Country)
print(result_pos)

    [City(continet='Asia', name='Tokyo', country='JP'), City(continet='Asia', name='Delhi', country='IN')]
    []
    JP
    IN
    [City(continet='Asia', name='Tokyo', country='JP'), City(continet='Asia', name='Delhi', country='IN')]