本章将学会OOP思想，定义类，方法，继承，多态

1、Python类

1.1、Objects（对象）

• 万物皆对象
• 比如我可以使用type()方法去检查对象类型

"""
<class 'int'>
<class 'list'>
<class 'tuple'>
<class 'dict'>
"""
print(type(1))
print(type([]))
print(type(()))
print(type({}))

1.2、Class(类)

• 可以认为这个一份蓝图或者模板
• 语法：class 类名: 属性和方法

# pass 表示没有任何实现
class Sample:
    pass

• init 内置构造初始化方法
• self 表示本对象

class Dog:
    # 类级别属性
    species = 'mammal'
    def __init__(self, breed, name):
        self.breed = breed
        self.name = name
sam = Dog('Lab', 'Sam')
print(Dog.species)


# 定义一个圆
class Circle:
    pi = 3.14

    # 圆默认半径为1
    def __init__(self, radius =1):
        self.radius = radius
        self.area = radius **2 * Circle.pi

    # 重新设置半径
    def setRadius(self, new_radius):
        self.radius = new_radius
        self.area = new_radius * new_radius * self.pi
    # 计算周长
    def getCircumference(self):
        return self.radius * self.pi * 2

c = Circle()
print('Radius is: ', c.radius)
print('Area is: ', c.area)
print('Circumference is: ', c.getCircumference())

# 重新设置半径为2
c.setRadius(2)
print('Radius is: ', c.radius)
print('Area is: ', c.area)
print('Circumference is: ', c.getCircumference())

1.2.1、继承（Inheritance)

• 语法： class 子类名(父类)

# Dog 继承Animal 的类， 重写whoAmI方法
class Animal:
    def __init__(self):
        print("Animal created")

    def whoAmI(self):
        print("Animal")

    def eat(self):
        print("Eating")

class Dog(Animal):
    def __init__(self):
        Animal.__init__(self)
        print("Dog created")

    def whoAmI(self):
        print('Dog')

    def bark(self):
        print("Woof!")
d = Dog()

d.whoAmI()

d.eat()
d.bark()

1.2.2、多态，同一个方法名，不同行为

# 比如 Dog 和Cat 叫声是不一样
class Dog:
    def __init__(self, name):
        self.name = name

    def speak(self):
        return self.name+ ' says Woof!'

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

    def speak(self):
        return self.name + ' says Meow!'

niko = Dog('Niko')
felix = Cat('Felix')
print(niko.speak())
print(felix.speak())

# 定义一个方法
def pet_speak(pet):
    print(pet.speak())


# 定义一个基类Animal
class Animal:
    def __init__(self, name):
        self.name = name
    def speak(self):
        raise NotImplementedError('Subclass must implement abstract method')
class Dog(Animal):
    def speak(self):
        return self.name + ' says Woof'

class Cat(Animal):

    def speak(self):
        return self.name + ' says Meow!'

fido = Dog('Fido')
isis = Cat('Isis')
print(fido.speak())
print(isis.speak())

1.2.3、重置内置函数

• 比如__str__ 重写tostring方法
• 重写len() 方法
• 重写del() 删除方法

# 特殊方法， 自带方法，可以重写
class Book:
    def __init__(self, title, author, pages):
        print('A book is created')
        self.title = title
        self.author = author
        self.pages = pages
    def __str__(self):
        return "Title: %s, author: %s, pages: %s" %(self.title, self.author, self.pages)

    def __len__(self):
        return self.pages

    def __del__(self):
        print("A book is destroyed")

book = Book("Python Rocks!", "Jose Portilla", 159)

print(book)
print(len(book))
del book

2、错误和异常捕获

我们需要异常信息提示整个系统完整性

2.1、语法

"""
try:
    捕获业务逻辑
except ExceptionI:
    如果是异常ExceptionI 执行如下block块
except ExceptionII:
    如果是异常ExceptionII，执行如下block块
else:
    如果没有异常执行如下代码块
finally:
    无论是否发现异常都会执行

"""
# 没有异常，它有写权限
try:
    f = open('testfile','w')
    f.write('Test write this')
except IOError:
    print("Error: Could not find file or read data")
else:
    print("Content written successfully")
    f.close()

# 读权限
try:
    f = open("testfile", 'r')
    f.write("Test write this")
except IOError:
    print("Error: Could not find file or read data")
else:
    print("Content written successfully")
    f.close()

2.2、finally 模块

• 语法

"""
try:
 代码块
finally:
 这段代码什么时候都会执行
"""
try:
    f = open("testfile", "w")
    f.write("Test write statement")
    f.close()
finally:
    print("Always execute finally code blocks")

# 直到输入正确的int的值
def askint():
    while True:
        try:
            val = int(input("Please enter an integer: "))
        except:
            print("Looks like you did not enter an integer!")
            continue
        else:
            print("Yep that's an integer")
            print(val)
            break
        finally:
            print("Finally, I executed!")

总结

1. Class 是一切对象的模板
2. 学习继承和实现定义：子类名(父类名)， 例如 class Cat(Animal) Cat 继承Animal的类
3. xxx 一般为内置的方法，例如__init__是构造函数的初始化方法
4. 学习异常捕获try语法 except方法