创建和使用类
创建Dog类
class Dog():
"""一次模拟小狗的简单尝试"""
def __init__(self, name, age):
"""初始化属性name和age"""
self.name = name
self.age = age
def sit(self):
"""模拟小狗被命令蹲下"""
print(self.name.title() + ' 现在蹲下!')
def roll_over(self):
"""模拟小狗被命令时打滚"""
print(self.name.title() + ' 打滚!')
分析下Dog类的结构:
"""一次模拟小狗的简单尝试"""文档注释, 可以放在类上, 也可以放在方法上- 方法
__init__()是构造方法, 它是一个特殊方法,在这个方法名称中, 开头和末尾各有两个下划线, 区别于其他方法, 当创建Dog()类的时候Python会自动运行它, 关于定义的三个形参(self, name, age), self代表类的实例，而非类, 当Python调用__init__()方法来创建实例时, 将自动的传入实参self, 每个与类相关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.
根据类创建实例
# 根据类创建实例
my_dog = Dog('哈士奇', 6)
# 访问属性 my_dog.name
print('我的狗名字是 ' + my_dog.name.title() + '.')
print('我的狗 ' + str(my_dog.age) + ' 岁了.')
# 调用方法
my_dog.sit()
my_dog.roll_over()
我的狗名字是 哈士奇.
我的狗 6 岁了.
哈士奇 现在蹲下!
哈士奇 打滚!
- 访问属性 my_dog.name
- 调用方法 my_dog.sit()
使用类和实例
Car类
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
# 给属性指定默认值
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回整洁的描述性信息"""
long_name = str(self.year) + ' ' + self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的消息"""
print('The Car has ' + str(self.odometer_reading) + ' miles on it.')
def update_odometer(self, mileage):
"""将里程表读数设置为指定的值"""
self.odometer_reading = mileage
def increment_odometer(self, miles):
self.odometer_reading += miles
测试一下:
my_new_car = Car('audi', 'a4', 2016)
print(my_new_car)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()
结果:
<__main__.Car object at 0x1037d8040>
2016 Audi A4
The Car has 0 miles on it.
给属性指定默认值
在上面构造方法中可以看到:
# 给属性指定默认值
self.odometer_reading = 0
修改属性的值
# 修改属性的值
my_new_car.odometer_reading = 23
my_new_car.read_odometer()
The Car has 23 miles on it.
通过方法修改属性的值
# 通过方法修改属性的值
my_new_car.update_odometer(30)
my_new_car.read_odometer()
The Car has 30 miles on it.
通过方法对属性的值进行递增
# 通过方法对属性的值进行递增
my_new_car.increment_odometer(10)
my_new_car.read_odometer()
The Car has 40 miles on it.
继承
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
# 给属性指定默认值
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回整洁的描述性信息"""
long_name = str(self.year) + ' ' + self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的消息"""
print('The Car has ' + str(self.odometer_reading) + ' miles on it.')
def update_odometer(self, mileage):
"""将里程表读数设置为指定的值"""
self.odometer_reading = mileage
def increment_odometer(self, miles):
self.odometer_reading += miles
def fill_gas_tank(self):
"""普通汽车有油箱"""
print('This Car need a gas tank!')
class Battery():
"""一次模拟电动汽车电瓶的简单尝试"""
def __init__(self, battery_size=70):
"""初始化电瓶属性"""
self.battery_size = battery_size
def describe_battery(self):
"""打印一条描述电瓶容量的消息"""
print('This Car has a ' + str(self.battery_size) + '-kwh battery.')
def get_range(self):
"""打印一条消息, 指出电瓶的续航里程"""
if self.battery_size == 70:
range = 240
elif self.battery_size == 85:
range= 270
message = 'This car can go approximately ' + str(range) + ' miles on a full charge.'
print(message)
class ElectricCar(Car):
"""
电动汽车的独特之处
"""
def __init__(self, make, model, year):
"""
初始化父类的属性
再初始化电动汽车特有的属性
"""
super().__init__(make, model, year)
# 将实例用作属性
self.battery = Battery()
def fill_gas_tank(self):
"""电动汽车没有油箱"""
print('This Car doesn‘s need a gas tank!')
上面代码中有两个类, 父类是Car, 子类是ElectricCar, ElectricCar(Car)就表示子类ElectricCar继承父类Car
子类的方法__init__()
def __init__(self, make, model, year):
super().__init__(make, model, year)
super()是一个特殊函数, 帮助Python将父类和子类关联起来
做一下测试:
my_tesla = ElectricCar('tesla', 'model s', 2016)
print(my_tesla.get_descriptive_name())
2016 Tesla Model S
重写父类的方法
def fill_gas_tank(self):
"""电动汽车没有油箱"""
print('This Car doesn‘s need a gas tank!')
做一下测试:
# 测试 重写父类的方法
my_tesla.fill_gas_tank()
This Car doesn‘s need a gas tank!
将实例用作属性
# 将实例用作属性
self.battery = Battery()
测试一下:
# 测试 将实例用作属性
my_tesla.battery.describe_battery()
my_tesla.battery.get_range()
This Car has a 70-kwh battery.
This car can go approximately 240 miles on a full charge.
导入类
导入单个类
car.py
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
# 给属性指定默认值
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回整洁的描述性信息"""
long_name = str(self.year) + ' ' + self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的消息"""
print('The Car has ' + str(self.odometer_reading) + ' miles on it.')
def update_odometer(self, mileage):
"""将里程表读数设置为指定的值"""
self.odometer_reading = mileage
def increment_odometer(self, miles):
self.odometer_reading += miles
my_car.py
# 导入单个类
from car import Car
my_new_car = Car('audi', 'a4', 2016)
print(my_new_car)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()
# 修改属性的值
my_new_car.odometer_reading = 23
my_new_car.read_odometer()
测试结果:
<car.Car object at 0x100659040>
2016 Audi A4
The Car has 0 miles on it.
The Car has 23 miles on it.
在一个模块中存储多个类
electric_car.py
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
# 给属性指定默认值
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回整洁的描述性信息"""
long_name = str(self.year) + ' ' + self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的消息"""
print('The Car has ' + str(self.odometer_reading) + ' miles on it.')
def update_odometer(self, mileage):
"""将里程表读数设置为指定的值"""
self.odometer_reading = mileage
def increment_odometer(self, miles):
self.odometer_reading += miles
def fill_gas_tank(self):
"""普通汽车有油箱"""
print('This Car need a gas tank!')
class Battery():
"""一次模拟电动汽车电瓶的简单尝试"""
def __init__(self, battery_size=70):
"""初始化电瓶属性"""
self.battery_size = battery_size
def describe_battery(self):
"""打印一条描述电瓶容量的消息"""
print('This Car has a ' + str(self.battery_size) + '-kwh battery.')
def get_range(self):
"""打印一条消息, 指出电瓶的续航里程"""
if self.battery_size == 70:
range = 240
elif self.battery_size == 85:
range= 270
message = 'This car can go approximately ' + str(range) + ' miles on a full charge.'
print(message)
class ElectricCar(Car):
"""
电动汽车的独特之处
"""
def __init__(self, make, model, year):
"""
初始化父类的属性
再初始化电动汽车特有的属性
"""
super().__init__(make, model, year)
# 将实例用作属性
self.battery = Battery()
def fill_gas_tank(self):
"""电动汽车没有油箱"""
print('This Car doesn‘s need a gas tank!')
从一个模块中导入多个类
# 从一个模块中导入多个类
from electric_car import ElectricCar, Car
导入整个模块
# 导入整个模块 需要使用 模块名.
import electric_car
my_new_car = electric_car.Car('audi', 'a4', 2016)
导入模块中所有的类
from electric_car import *
Python 标准库
Python 标准库是一组模块, 安装Python都包含它.
下面演示使用标准库中collections模块的类OrderedDict
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, languages in favorite_languages.items():
print(name.title() + "'s favorite languages is " + languages.title() + '.')
Jen's favorite languages is Python.
Sarah's favorite languages is C.
Edward's favorite languages is Ruby.
Phil's favorite languages is Python.
Python3 目录