python/day04/class_basics.py

"""class_basics.py - Python 类基础示例

涵盖：类定义、对象实例化、__init__、属性、方法、实例方法、类方法、静态方法、
继承、封装和多态等基础知识。
"""
from abc import ABC, abstractmethod


class Person:
    """定义一个简单的类。"""

    # 类属性
    species = "Human"

    def __init__(self, name: str, age: int):
        """构造方法：初始化实例属性。"""
        self.name = name
        self.age = age

    def speak(self)-> str:
        """实例方法：访问实例属性。"""
        return f"My name is {self.name}, I am {self.age} years old."

    @classmethod
    def from_birth_year(cls, name: str, birth_year: int)-> 'Person':
        """类方法：根据出生年份计算年龄。"""
        age = 2026 - birth_year
        return cls(name, age)

    @staticmethod
    def is_adult(age: int)-> bool:
        """静态方法：不访问实例或类状态。"""
        return age >= 18


# 继承示例
class Student(Person):
    def __init__(self, name: str, age: int, school: str):
        super().__init__(name, age)
        self.school = school

    def study(self):
        return f"{self.name} is studying at {self.school}."


class  Animal(ABC):
    @abstractmethod
    def speak(self):
       pass

# 多态示例
class Dog(Animal):
    def speak(self):
        return "Woof!"


class Cat(Animal):
    def speak(self):
        return "Meow!"


# 封装示例：使用单下划线表示受保护属性
class BankAccount:
    def __init__(self, balance):
        self._balance = balance

    def get_balance(self):
        return self._balance

    def deposit(self, amount):
        if amount > 0:
            self._balance += amount


# 类属性访问
print("Person.species ->", Person.species)

# 实例化对象
p1 = Person("Alice", 20)
print("p1.speak() ->", p1.speak())

# 类方法调用
p2 = Person.from_birth_year("Bob", 2005)
print("p2.speak() ->", p2.speak())

# 静态方法调用
print("Person.is_adult(21) ->", Person.is_adult(21))

# 继承
s1 = Student("Charlie", 19, "Harvard")
print("s1.study() ->", s1.study())
print("s1.speak() ->", s1.speak())

# 多态
animals = [Dog(), Cat()]
for animal in animals:
    print("animal.speak() ->", animal.speak())

# 封装
account = BankAccount(1000)
print("account.get_balance() ->", account.get_balance())
account.deposit(200)
print("after deposit ->", account.get_balance())

# 对象的属性访问
print("p1.name ->", p1.name)

# 使用 __dict__ 查看实例属性
print("p1.__dict__ ->", p1.__dict__)

# 说明：
# - 类是对象的模板
# - 实例是类创建出来的对象
# - self 表示当前实例
# - __init__ 是初始化方法
# - 继承允许子类复用父类功能
# - 多态允许不同对象用同一接口表现不同行为