类与面向对象

class Dog:
    """A simple dog class."""
    kind = "canine"          # 类变量，所有实例共享

    def __init__(self, name):
        self.name = name     # 实例变量

    def bark(self):
        print(f"{self.name}: Woof!")

d = Dog("Rex")
d.bark()  # Rex: Woof!

class Dog:
    tricks = []              # 类变量（共享）
    def __init__(self, name):
        self.name = name

d1 = Dog("A"); d2 = Dog("B")
d1.tricks.append("sit")
print(d2.tricks)  # ['sit']  ← 共享陷阱！

class Dog:
    def __init__(self, name):
        self.name = name
        self.tricks = []     # 实例变量

class Animal:
    def __init__(self, name):
        self.name = name

    def speak(self):
        raise NotImplementedError

class Cat(Animal):
    def speak(self):
        return f"{self.name}: Meow"

class Dog(Animal):
    def speak(self):
        return f"{self.name}: Woof"

class Vehicle:
    def start(self):
        print("vehicle start")

class Car(Vehicle):
    def start(self):
        super().start()         # 调用父类
        print("car start")

Car().start()

class A:    pass
class B:    pass
class C(A, B): pass

print(C.__mro__)    # 方法解析顺序

class Vector:
    def __init__(self, x, y):
        self.x, self.y = x, y

    def __repr__(self):
        return f"Vector({self.x}, {self.y})"

    def __eq__(self, other):
        return self.x == other.x and self.y == other.y

    def __add__(self, other):
        return Vector(self.x + other.x, self.y + other.y)

    def __len__(self):
        return 2

    def __getitem__(self, i):
        return (self.x, self.y)[i]

v1 = Vector(1, 2)
v2 = Vector(3, 4)
v1 + v2        # Vector(4, 6)
len(v1)        # 2

class Counter:
    count = 0

    @classmethod
    def show_count(cls):
        return cls.count

    @staticmethod
    def help():
        return "Counter counts things"

    @property
    def doubled(self):
        return self.count * 2

class Counter:
    def __init__(self, n):
        self.i, self.n = 0, n
    def __iter__(self):
        return self
    def __next__(self):
        if self.i >= self.n:
            raise StopIteration
        self.i += 1
        return self.i

list(Counter(3))   # [1, 2, 3]

def counter(n):
    for i in range(1, n + 1):
        yield i

from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int

p = Point(1, 2)
print(p)         # Point(x=1, y=2)