2022年5月21日学习笔记

　　Python学习笔记 第九章 类一、创建和使用类二、使用类和实例三、继承四、导入模块五、Python标准库六、注
　　一、创建和使用类
　　1、类和函数的区别
　　类（class）：类是面向你对象的，class可以保存一此属性的状态，同时也起到模板的作用，把一些通用的东西写进类定义中，也就是在’init’中。class有点像是将多个函数进行功能性封装
　　函数：函数更像是面向过程编程，更易理解，但是当系统较大时，重复性就会增多。
　　使用class Name() 来创建一个Name类，类中包含许多方法（函数），根据类来创建实例XingMing = Name()，实例可以用句点表示法调用类中的方法。
　　一个类包含了一系列实例的通性，众多根据类创建的实例可以使用句点表示法调用类中的方法。
　　2、创建Dog类class Dog():  def __init__(self,name,age):   self.name = name   self.age = age  def sit(self):   print(self.name.title() + ＂ is now sitting.＂)  def roll_over(self):   print(self.name.title() + ＂ rolled over!＂) my_dog = Dog(＂willie＂, 6) print(＂My dog＂s name is ＂ + my_dog.name.title() + ＂.＂) print(＂My dog is ＂ + str(my_dog.age) + ＂ years old.＂) my_dog.sit() my_dog.roll_over()  输出结果为： My dog＂s name is Willie. My dog is 6 years old. Willie is now sitting. Willie rolled over!在Python中，首字母大写的名称指的是类，因为要从空白创建这个类，所以类定义中的括号是空的。 _ init _ ()是类中的默认方法，每次根据类创建实例时，Python都会自动运行它。 形参self必不可少，Python调用_ init _()方法来创建实例时，将自动传入实参self。每个与类相关联的方法调用都自动传递实参self，它是一个指向实例本身的引用，让实例能够访问类中的属性和方法。 创建Dog实例时，Python将diaoyongDog类的方法_ init _()，通过实参向Dog()传递名字和年龄；self会自动传递，因此我们不需要传递它。每当我们根据Dog类创建实例时，都只需给最后两个形参（name和age）提供值。 以self为前缀的变量都可供类中的所有方法使用，可以通过类的任何实例来访问这些变量。 像self.name、self.age这样可以通过实例访问的变量称为属性。 属性参数传递给_ init _，使用self.属性来给实例赋予属性。 访问属性 ：my_dog.name，Python先找到实例my_dog，再查找与这个实例相关联的属性。 调用方法 ：my_dog.sit()。 创建实例后，以实例名替代self，如my_dog.name相当于self.name。 class People():  def __init__(self, name, age, weight):   self.name = name   self.age = age   self.weight = weight  def walk(self):   print(self.name.title() + ＂ is now walking on the road.＂)  def die(self):   print(self.name.title() + ＂＂s weight is ＂ + str(self.weight) + ＂ when he was sent to the crematorium.＂) zhang = People(＂Zhang San＂, 18, 200) print(zhang.name.title() + ＂ is ＂ + str(zhang.age) + ＂ years old.＂) zhang.walk() zhang.die()  输出结果为： Zhang San is 18 years old. Zhang San is now walking on the road. Zhang San＂s weight is 200 when he was sent to the crematorium.二、使用类和实例
　　1、Car类 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title() my_new_car = Car(＂audi＂, ＂a4＂, 2016) print(my_new_car.get_descriptive_name())  输出结果为： 2016 Audi A4.
　　2、给属性指定默认值 直接在方法中创建一个变量，并赋予初始默认值 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 0 #赋予默认值0  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂) my_new_car = Car(＂audi＂, ＂a4＂, 2016) print(my_new_car.get_descriptive_name()) my_new_car.read_odometer()  输出结果为： 2016 Audi A4. This car has 0 miles on it.也可像给形参赋予默认值一样：（更易理解） class Car():  def __init__(self,make,model,year,odometer_reading=0):   self.make = make   self.model = model   self.year = year   self.odometer_reading = odometer_reading  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂) my_new_car = Car(＂audi＂, ＂a4＂, 2016) print(my_new_car.get_descriptive_name()) my_new_car.read_odometer()  输出结果： 2016 Audi A4. This car has 0 miles on it.
　　3、直接修改属性的值 可在类外直接对该变量进行赋值，此时Python会使用新赋予的值而非默认值 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 0 #赋予默认值0  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂) my_new_car = Car(＂audi＂, ＂a4＂, 2016) my_new_car.odometer_reading = 23 print(my_new_car.get_descriptive_name()) my_new_car.read_odometer()  输出结果为： 2016 Audi A4. This car has 23 miles on it.也可在定义实例时直接传入实参 class Car():  def __init__(self,make,model,year,odometer_reading=0):   self.make = make   self.model = model   self.year = year   self.odometer_reading = odometer_reading  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂) my_new_car = Car(＂audi＂, ＂a4＂, 2016,23) print(my_new_car.get_descriptive_name()) my_new_car.read_odometer()  输出结果为： 2016 Audi A4. This car has 23 miles on it.通过方法修改属性的值 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 10 #赋予默认值10  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂)  def update_odometer(self,mileage):   if mileage >= self.odometer_reading:    self.odometer_reading = mileage   else:    print(＂You can＂t roll back an odometer!＂) my_new_car = Car(＂audi＂, ＂a4＂, 2016) my_new_car.update_odometer(5) print(my_new_car.get_descriptive_name()) my_new_car.read_odometer()  输出结果为： You can＂t roll back an odometer! 2016 Audi A4. This car has 10 miles on it.通过方法对属性的值进行递增 class Car():  def __init__(self,make,model,year):  self.make = make  self.model = model  self.year = year  self.odometer_reading = 10 #赋予默认值10  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂)  def update_odometer(self,mileage):   if mileage >= self.odometer_reading:    self.odometer_reading = mileage   else:    print(＂You can＂t roll back an odometer!＂)  def increment_odometer(self,miles):   if miles >= 0:    self.odometer_reading +=miles   else:    print(＂You can＂t roll back an odometer!＂) my_used_car = Car(＂audi＂, ＂a4＂, 2016) print(my_used_car.get_descriptive_name()) my_used_car.update_odometer(23500) my_used_car.read_odometer() my_used_car.increment_odometer(100) my_used_car.read_odometer()  输出结果为： 2016 Audi A4. This car has 23500 miles on it. This car has 23600 miles on it.三、继承编写类时，并非总要从空白开始，若要编写的类时另一个线现成类的特殊版本，可使用继承。 一个类继承另一个类时，它将自动获得另一个类的所有属性和方法，原有的类称为父类，而新类称为子类。 子类继承了其父类的所有属性和方法，同时还可以定义自己的属性和方法。 继承：类括号非空白，使用super()函数关联父子类。
　　1、子类的方法_ init _() 创建子类的实例时，Python首先需要完成的任务是给父类的所有属性赋值。 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 10 #赋予默认值10  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂)  def update_odometer(self,mileage):   if mileage >= self.odometer_reading:    self.odometer_reading = mileage   else:    print(＂You can＂t roll back an odometer!＂)  def increment_odometer(self,miles):   if miles >= 0:    self.odometer_reading +=miles   else:    print(＂You can＂t roll back an odometer!＂) class ElectricCar(Car):  def __init__(self,make,model,year):   super().__init__(make, model, year) my_tesla = ElectricCar(＂tesla＂,＂model s＂,2016) print(my_tesla.get_descriptive_name())  输出结果为： 2016 Tesla Model S.创建子类时，父类必须包含在当前文件中，且位于子类前面。 定义子类时，必须在括号内指定父类的名称：ElectricCar(Car)。 super()是一个特殊函数，帮助Python将父类与子类关联起来。 super()._ init  (make, model, year) 这行代码让Python调用ElectricCar的父类的方法  init _(),让ElectricCar实例包含父类的所有属性，父类也成为超类(superclass)。
　　2、给子类定义属性和方法 让一个类继承另一类后，可添加区分子类和父类所需的新属性和方法。 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 10 #赋予默认值10  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂)  def update_odometer(self,mileage):   if mileage >= self.odometer_reading:    self.odometer_reading = mileage   else:    print(＂You can＂t roll back an odometer!＂)  def increment_odometer(self,miles):   if miles >= 0:    self.odometer_reading +=miles   else:    print(＂You can＂t roll back an odometer!＂) class ElectricCar(Car):  def __init__(self,make,model,year):   super().__init__(make, model, year)   self.battery_size = 70  def describe_battery(self):   print(＂This car has a ＂ + str(self.battery_size) + ＂-kwh battery.＂) my_tesla = ElectricCar(＂tesla＂,＂model s＂,2016) print(my_tesla.get_descriptive_name()) my_tesla.describe_battery()  输出结果为： 2016 Tesla Model S. This car has a 70-kwh battery.
　　3、重写父类的方法 对于父类的方法，只要它不符合子类模拟的实物的行为，都可对其进行重写。 可在子类中定义一个与要重写的父类方法同名的方法，这样Python将不会考虑这个父类方法，而只关注在子类中定义的相应方法。 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 10 #赋予默认值10  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂)  def update_odometer(self,mileage):   if mileage >= self.odometer_reading:    self.odometer_reading = mileage   else:    print(＂You can＂t roll back an odometer!＂)  def increment_odometer(self,miles):   if miles >= 0:    self.odometer_reading +=miles   else:    print(＂You can＂t roll back an odometer!＂)  def fill_gas_tank(self):   print(＂This car doesn＂t need a gas tank!＂) class ElectricCar(Car):  def __init__(self,make,model,year):   super().__init__(make, model, year)   self.battery_size = 70  def describe_battery(self):   print(＂This car has a ＂ + str(self.battery_size) + ＂-kwh battery.＂)  def fill_gas_tank(self):   print(＂This car doesn＂t need a gas tank!＂) my_tesla = ElectricCar(＂tesla＂,＂model s＂,2016) print(my_tesla.get_descriptive_name()) my_tesla.describe_battery() my_tesla.fill_gas_tank()  输出结果为： 2016 Tesla Model S. This car has a 70-kwh battery. This car doesn＂t need a gas tank!
　　4、将实例用作属性 将一个大型类拆分成多个协同工作的小类，并将这些小类的实例用作其他类的一个属性。 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 10 #赋予默认值10  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂)  def update_odometer(self,mileage):   if mileage >= self.odometer_reading:    self.odometer_reading = mileage   else:    print(＂You can＂t roll back an odometer!＂)  def increment_odometer(self,miles):   if miles >= 0:    self.odometer_reading +=miles   else:    print(＂You can＂t roll back an odometer!＂)  def fill_gas_tank(self):   print(＂This car doesn＂t need a gas tank!＂)   class Battery():  def __init__(self,battery_size=70):   self.battery_size = battery_size  def describe_battery(self):   print(＂This car has a ＂ + str(self.battery_size) + ＂-kwh battery.＂) class ElectricCar(Car):  def __init__(self,make,model,year):   super().__init__(make, model, year)   self.battery = Battery()  def fill_gas_tank(self):   print(＂This car doesn＂t need a gas tank!＂) my_tesla = ElectricCar(＂tesla＂,＂model s＂,2016) print(my_tesla.get_descriptive_name()) my_tesla.fill_gas_tank() my_tesla.battery.describe_battery()  输出结果为： 2016 Tesla Model S. This car doesn＂t need a gas tank! This car has a 70-kwh battery.在其他类中使用实例作为属性：self.类，然后再定义实例时：name.类.function即可。 slef.battery让Python创建一个新的Battery实例(由于没有指定尺寸，因此为默认值70)，并将该实例存储在属性self.battery中。 每当方法_ init _()被调用时，都将执行该操作；因此现在每个ElectricCar实例都包含一个自动创建的Battery实例。 my_tesla.battery.describe_battery()让Python在实例my_tesla中查找属性battery，并对存储在该属性中的Battery实例调用方法describe_battery()。
　　5、根据电池容量修改续航里程 class Car():  def __init__(self,make,model,year):   self.make = make   self.model = model   self.year = year   self.odometer_reading = 10 #赋予默认值10  def get_descriptive_name(self):   long_name = str(self.year) + ＂ ＂ + self.make +＂ ＂ + self.model + ＂.＂   return long_name.title()  def read_odometer(self):   print(＂This car has ＂ + str(self.odometer_reading) + ＂ miles on it.＂)  def update_odometer(self,mileage):   if mileage >= self.odometer_reading:    self.odometer_reading = mileage   else:    print(＂You can＂t roll back an odometer!＂)  def increment_odometer(self,miles):   if miles >= 0:   self.odometer_reading +=miles  else:   print(＂You can＂t roll back an odometer!＂)  def fill_gas_tank(self):   print(＂This car doesn＂t need a gas tank!＂) class Battery():  def __init__(self,battery_size=70):   self.battery_size = battery_size  def describe_battery(self):   print(＂This car has a ＂ + str(self.battery_size) + ＂-kwh battery.＂)  def get_range(self):   if self.battery_size == 70:    range = 240   elif self.battery_size == 85:    range = 270 message = ＂This car can go approximately ＂ + str(range) message +=＂ miles on a full charge. ＂ print(message) class ElectricCar(Car):  def __init__(self,make,model,year):   super().__init__(make, model, year)   self.battery = Battery()  def fill_gas_tank(self):   print(＂This car doesn＂t need a gas tank!＂) my_tesla = ElectricCar(＂tesla＂,＂model s＂,2016) print(my_tesla.get_descriptive_name()) my_tesla.fill_gas_tank() my_tesla.battery = Battery(85) #修改电池默认值 my_tesla.battery.describe_battery() my_tesla.battery.get_range()  输出结果为： 2016 Tesla Model S. This car doesn＂t need a gas tank! This car has a 85-kwh battery. This car can go approximately 270 miles on a full charge.四、导入模块与从其他模块导入函数方法一致 五、Python标准库from collections import OrderedDict favorite_languages = OrderedDict() favorite_languages[＂jen＂] = ＂python＂ favorite_languages[＂sarah＂] = ＂c＂ favorite_languages[＂edward＂] = ＂ruby＂ favorite_languages[＂phil＂] = ＂python＂ for name , language in favorite_languages.items():  print(name.title() + ＂＂s favorite language is ＂ + language.title() + ＂.＂)  输出结果为： Jen＂s favorite language is Python. Sarah＂s favorite language is C. Edward＂s favorite language is Ruby. Phil＂s favorite language is Python.字典能将信息关联起来，但不记录添加键-值对的顺序。 使用collections中的OrderedDict类可以创建字典并记录其中的键-值对的添加顺序。 六、注类名单词首字母大写，不使用下划线；实例名和模块名都采用小写，单词之间加上下划线。 每个类后都应紧定义一个文档字符串简要描述类的功能。 用一个空行分隔方法，用两个空行分隔类。