第四章练习答案

00-classes-and-instances

练习 1：Person类

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def greet(self):
        return f"Hello, I'm {self.name} and I'm {self.age} years old"

person = Person("Alice", 30)
print(person.greet())

练习 3：类属性计数器

class Counter:
    count = 0
    
    def __init__(self):
        Counter.count += 1

c1 = Counter()
c2 = Counter()
print(Counter.count)  # 2

01-inheritance-and-mro

练习 1：形状继承

import math

class Shape:
    def area(self):
        raise NotImplementedError

class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius
    
    def area(self):
        return math.pi * self.radius ** 2

class Rectangle(Shape):
    def __init__(self, width, height):
        self.width = width
        self.height = height
    
    def area(self):
        return self.width * self.height

02-special-methods

练习 1：实现__eq__

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def __eq__(self, other):
        if not isinstance(other, Point):
            return False
        return self.x == other.x and self.y == other.y

p1 = Point(1, 2)
p2 = Point(1, 2)
print(p1 == p2)  # True

03-properties-and-descriptors

练习 1：温度转换

class Temperature:
    def __init__(self, celsius):
        self._celsius = celsius
    
    @property
    def celsius(self):
        return self._celsius
    
    @celsius.setter
    def celsius(self, value):
        self._celsius = value
    
    @property
    def fahrenheit(self):
        return self._celsius * 9/5 + 32
    
    @fahrenheit.setter
    def fahrenheit(self, value):
        self._celsius = (value - 32) * 5/9

temp = Temperature(0)
print(temp.fahrenheit)  # 32.0
temp.fahrenheit = 212
print(temp.celsius)  # 100.0

04-dataclasses

练习 1：Product类

from dataclasses import dataclass

@dataclass
class Product:
    name: str
    price: float
    quantity: int = 0
    
    def total_value(self):
        return self.price * self.quantity

product = Product("Laptop", 999.99, 5)
print(product.total_value())  # 4999.95

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