面向对象基础与动态特性

Python 中通过 class 关键字构建自定义类型。实例化时，解释器自动触发构造逻辑完成对象初始化。

class Human:
    def __init__(self, nickname):
        self.nickname = nickname

    def display(self):
        print(f"当前对象: {self.nickname}")

if __name__ == '__main__':
    h = Human("Alice")
    h.display()

运行时属性注入

Python 允许在实例创建后动态挂载属性，但该属性仅属于被操作的实例，不会扩散到其他对象。

class Human:
    def __init__(self):
        pass

if __name__ == '__main__':
    h = Human()
    h.nickname = "Alice"
    print(h.nickname)

组合模式

类的成员可以是另一个类的实例，形成"has-a"关系。

class Engine:
    def __init__(self, power):
        self.power = power

class Vehicle:
    def __init__(self, engine):
        self.engine = engine

v8 = Engine(450)
car = Vehicle(v8)

核心魔术方法详解

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

    def __str__(self):
        return f"Student({self.name!r})"

    def __repr__(self):
        return f"Student(name={self.name!r})"

    def __len__(self):
        return len(self.name)

    def __getitem__(self, idx):
        return self.name[idx]

if __name__ == '__main__':
    s = Student("Bob")
    print(s)           # Student('Bob')
    print(len(s))      # 3
    print(s[0])        # B

运算符重载机制

算术运算符

比较运算符

一元运算符重载应返回新对象，而非修改操作数本身。

class Vector:
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

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

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

    def __mul__(self, scalar):
        return Vector(self.x * scalar, self.y * scalar)

    def __call__(self):
        print(f"向量坐标: ({self.x}, {self.y})")

v1 = Vector(2, 3)
v2 = Vector(1, 1)
print(v1 + v2)      # Vector(3, 4)
print(v1 * 3)       # Vector(6, 9)
v1()                # 向量坐标: (2, 3)

访问控制与封装

命名约定与可见性

class Employee:
    company = "TechCorp"      # 类属性，公有

    def __init__(self, name, salary):
        self.name = name
        self.__salary = salary   # 名称改写为 _Employee__salary

    def get_salary(self):
        return self.__salary

    def set_salary(self, value):
        if value > 0:
            self.__salary = value

    def __audit(self):           # 私有方法
        print("内部审计中...")

    def public_audit(self):
        self.__audit()

e = Employee("Tom", 5000)
print(e.name)           # Tom
print(e.get_salary())   # 5000
e.set_salary(6000)

继承体系设计

单继承与属性继承

class Base:
    def __init__(self, value):
        self.value = value
        self.__hidden = 100

class Derived(Base):
    def __init__(self, value, extra):
        super().__init__(value)   # 显式调用父类初始化
        self.extra = extra

d = Derived(10, 20)
print(d.value)          # 10
print(d._Base__hidden)  # 100 (名称改写访问，不推荐)

多继承与 MRO

class A:
    def __init__(self):
        print("A init")
        super().__init__()

class B(A):
    def __init__(self):
        print("B init")
        super().__init__()

class C(A):
    def __init__(self):
        print("C init")
        super().__init__()

class D(B, C):
    def __init__(self):
        print("D init")
        super().__init__()

print(D.__mro__)
# (<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.A'>, <class 'object'>)
d = D()

方法重写与扩展

class Logger:
    def log(self, msg):
        print(f"[INFO] {msg}")

class TimestampLogger(Logger):
    def log(self, msg):
        from datetime import datetime
        super().log(f"{datetime.now()}: {msg}")

tl = TimestampLogger()
tl.log("系统启动")

多态与类方法

class Dog:
    def speak(self):
        print("汪汪")

class Cat:
    def speak(self):
        print("喵喵")

def animal_sound(creature):
    creature.speak()

animal_sound(Dog())   # 汪汪
animal_sound(Cat())   # 喵喵

类方法与静态方法

class MathUtils:
    PI = 3.14159

    @classmethod
    def circle_area(cls, radius):
        return cls.PI * radius ** 2

    @staticmethod
    def is_positive(num):
        return num > 0

print(MathUtils.circle_area(5))    # 78.53975
print(MathUtils.is_positive(-3))   # False

模块组织与导入

# utils.py
threshold = 10

def helper():
    return "辅助功能"

class Tool:
    pass

# main.py
import utils
from utils import Tool, helper

# 处理命名冲突
import utils as u
def helper():
    pass

print(u.helper())   # 调用模块中的函数

Property 描述符

类属性方式

class Product:
    def __init__(self):
        self.__price = 0.0

    def get_price(self):
        return self.__price

    def set_price(self, value):
        if value >= 0:
            self.__price = value

    price = property(get_price, set_price)

p = Product()
p.price = 99.5
print(p.price)

装饰器方式（推荐）

class Product:
    def __init__(self):
        self.__price = 0.0

    @property
    def price(self):
        return self.__price

    @price.setter
    def price(self, value):
        if value >= 0:
            self.__price = value

    @price.deleter
    def price(self):
        del self.__price

p = Product()
p.price = 149.0
print(p.price)

魔术方法分类速查