第 9 章主要讲的类，这个之前在 shell 中没遇到过
一直运用的也不是很溜，不过多敲多练，应该会有进步吧
创建类和使用类
创建一个 Dog 类
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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)
my_dog.sit()
my_dog.roll_over()
print("My dog‘s name is " + my_dog.name.title() + ".")
print("My dog is " + str(my_dog.age) + " years old.")
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Willie is now sitting.
Willie rolled over!
My dog‘s name is Willie.
My dog is 6 years old.
创建多个实例
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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)
your_dog = Dog(‘lucy‘, 3)
print("My dog‘s name is " + my_dog.name.title() + ".")
print("My dog is " + str(my_dog.age) + " years old.")
my_dog.sit()
print("\nYour dog‘s name is " + your_dog.name.title() + ".")
print("Your dog is " + str(your_dog.age) + " years old.")
your_dog.sit()
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My dog‘s name is Willie.
My dog is 6 years old.
Willie is now sitting.
Your dog‘s name is Lucy.
Your dog is 3 years old.
Lucy is now sitting.
Car 类练习
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
def get_descriptive_name(self):
long_name = self.year + ‘ ‘ + self.make + ‘ ‘ + str(self.model)
return long_name.title()
my_new_car = Car(‘audi‘, 24, ‘2016‘)
print(my_new_car.get_descriptive_name())
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2016 Audi 24
添加属性默认值
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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‘, ‘24‘, ‘2016‘)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()
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2016 Audi 24
This car has 0 miles on it.
修改属性的值
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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‘, ‘24‘, ‘2016‘)
print(my_new_car.get_descriptive_name())
my_new_car.odometer_reading = 23
my_new_car.read_odometer()
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2016 Audi 24
This car has 23 miles on it.
通过方法修改属性的值
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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):
self.odometer_reading = mileage
my_new_car = Car(‘audi‘, ‘24‘, ‘2016‘)
print(my_new_car.get_descriptive_name())
my_new_car.update_odometer(45)
my_new_car.read_odometer()
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2016 Audi 24
This car has 45 miles on it.
通过方法对属性的值进行递增
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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):
self.odometer_reading += miles
my_used_car = Car(‘subaru‘, ‘outback‘, 2013)
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()
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2013 Subaru Outback
This car has 23500 miles on it.
This car has 23600 miles on it.
继承 : 子类的方法 __init__( )
父类必须包含在当前文件中，且位于子类前面
定义子类时，括号中必须指定父类的名称
super( ) 是一个特殊函数，将父类和子类关联起来，让 ElectricCar 实例包含父类的所有属性
父类也称为超类。
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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):
self.odometer_reading += miles
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())
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2016 Tesla Model S
给子类定义属性和方法
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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):
self.odometer_reading += miles
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()
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2016 Tesla Model S
This car has a 70-kWh battery.
重写父类的方法
假设 Car 类中有一个名为 fill_gas_tank( ) 的函数，但是它对电动汽车毫无意义
可以在子类中重写该函数，Python就会运转子类中的代码，
而且还会保留父类中的其他函数
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def fill_gas_tank():
print("This car doesn‘t need a gas tank")
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将实例用作属性
新建一个 class Battery() 的类
在 class ElectricCar(Car) 类中指定 class Battery()
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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):
self.odometer_reading += miles
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()
my_tesla = ElectricCar(‘tesla‘, ‘model s‘, ‘year‘)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()
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2016 Tesla Model S
This car has a 70-kWh battery.
导入单个类
my_car.py导入car.py中的 Car 类
car.py 文件内容如下
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class Car():
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = str(self.year) + ‘ ‘ + self.make + ‘ ‘ + str(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):
self.odometer_reading += miles
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my_car.py 文件内容如下
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from car import Car
my_new_car = Car(‘audi‘, ‘24‘, 2016)
print(my_new_car.get_descriptive_name())
my_new_car.odometer_reading = 23
导入模块中的类
从 car.py 文件中导入 ElectricCar 类
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from car import ElectricCar
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导入模块中的多个类
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from car import ElectricCar, Car
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导入整个模块
直接导入 car.py 文件中全部函数
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import car
my_beetle = car.Car(‘volkswagen’, ‘beetle’)
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Python标准库
collections 模块中的 OrderedDict 类
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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() + ".")
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Jen‘s favorite language is Python.
Sarah‘s favorite language is C.
Edward‘s favorite language is Ruby.
Phil‘s favorite language is Python.