基于类创建对象时,每个对象都自动具备这种通用行为,然后根据需要赋予每个对象独特的个性。
根据类来创建对象被称为实例化,这让你能够使用类的实例。
1、方法__init__()
类中的函数称为方法,函数的一切都适用于方法。
访问属性:要访问实例的属性,可使用句点法:my_dog.name
调用方法: 实例 = class_name(实参)--->实例.function_name()
class Dog():
'''一次模拟小狗的简单尝试'''
def __init__(self, name, age): #类似于构造函数
self.name = name
self.age = age
def sit(self):
"""模拟小狗被命令时蹲下"""
print(self.name.title() + "is sitting now")
def roll_over(self):
"""模拟小狗被命令时打滚"""
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()
>>>My dog's name is Willie.
My dog is 6 years old.
Willie is sitting now
Willie rolled over !
使用类和实例:
给属性指定默认值:类中的每个属性都必须有初始值,哪怕是0或者空字符串。设置默认值时,在方法__init__()内指定这种初始值是可行的,且无需包含为它提供初始值的形参。
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, maker, model, year ):
"""初始化描述汽车的属性"""
self.maker = maker
self.model = model
self.year = year
self.odometer_reading = 160
def get_descriptive_name(self):
"""返回的整洁性的描述信息"""
long_time = str(self.year) + " " + self.maker + " " + self.model
return long_time.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()
>>>2016 Audi A4
This car has 160 miles on it.
修改属性的值:
直接通过实例进行修改:
my_new_car.odometer_reading = 23
通过方法进行设置:
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, maker, model, year, mileage):
"""初始化描述汽车的属性"""
self.maker = maker
self.model = model
self.year = year
self.mileage = mileage
def get_descriptive_name(self):
"""返回的整洁性的描述信息"""
long_time = str(self.year) + " " + self.maker + " " + self.model
return long_time.title()
def update_odometer(self):
print("This car has " + str(self.mileage) + " miles on it.")
my_new_car = Car('audi', 'a4', 2016, 1222)
print(my_new_car.get_descriptive_name())
通过方法进行递增(增加特定的值):
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, maker, model, year, mileage):
"""初始化描述汽车的属性"""
self.maker = maker
self.model = model
self.year = year
self.mileage = mileage
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回的整洁性的描述信息"""
long_time = str(self.year) + " " + self.maker + " " + self.model
return long_time.title()
def read_odometer(self):
"""打印一条指出汽车里程的信息"""
print("This car has " + str(self.odometer_reading) + " miles on it.")
def update_odometer(self, mileage):
print("This car has " + str(self.mileage) + " miles on it.")
def increment(self, miles):
self.odometer_reading += miles
my_used_car = Car('subaru', 'outback', 2013, 1010)
my_used_car.update_odometer(1010)
my_used_car.increment(100)
my_used_car.read_odometer()
print(my_used_car.get_descriptive_name())
>>> This car has 1010 miles on it.
This car has 100 miles on it.
2013 Subaru Outback
2、继承
编写类时,并非总是要从空白开始。让一个你要编写的类是另一个现成类的特殊版本,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,新类为子类。
子类继承了父类所有属性和方法,同时还可定义自己的属性和方法。
子类的方法__init__():
创建子类的实例时,python首先需要完成的认为是给父类的所有属性赋值。为此,子类的方法__init__()需要父类施以援手。
super是一个特殊函数,帮助python将父类和子类联系起来。父类也称为超类(superclass)
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self, maker, model, year):
"""初始化描述汽车的属性"""
self.maker = maker
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回的整洁性的描述信息"""
long_time = str(self.year) + " " + self.maker + " " + self.model
return long_time.title()
def read_odometer(self):
"""打印一条指出汽车里程的信息"""
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(self, miles):
self.odometer_reading += miles
class ElectricCar(Car):
"""电动车的独特之处"""
def __init__(self, make, model, year):
"""初始化父类"""
super(ElectricCar, self).__init__(make, model, year ) #super是一个特殊函数,将父类和子类联系起来
my_tesla = ElectricCar('tesla', 'model s', 2018)
print(my_tesla.get_descriptive_name())
>>>
2018 Tesla Model S
给子类定义属性和方法:可区分父类和子类
class ElectricCar(Car):
"""电动车的独特之处"""
def __init__(self, make, model, year):
"""初始化父类"""
super(ElectricCar, self).__init__(make, model, year ) #super是一个特殊函数,将父类和子类联系起来
self.battery_size = 70 ###新增属性
def describe_battery(self):
print("This car has a " + str(self.battery_size) + "-KWh battery")
my_tesla = ElectricCar('tesla', 'model s', 2018)
print(my_tesla.get_descriptive_name())
my_tesla.describe_battery()
>>>
2018 Tesla Model S
This car has a 70-KWh battery
重写父类方法:
对于父类的方法,只要它不符合子类模拟的实物的行为,都可以对其进行重写。
在子类中定义这样一个方法,即它与要写的父类方法同名。
class ElectricCar(Car):
"""电动车的独特之处"""
def __init__(self, make, model, year):
"""初始化父类"""
super(ElectricCar, self).__init__(make, model, year ) #super是一个特殊函数,将父类和子类联系起来
self.battery_size = 70
def describe_battery(self):
print("This car has a " + str(self.battery_size) + "-KWh battery")
######方法重写#########
def fill_gas_tank(self):
"""电动汽车没有油箱"""
print("This car doesn't have a gas tank!")
my_tesla = ElectricCar('tesla', 'model s', 2018)
print(my_tesla.get_descriptive_name())
my_tesla.describe_battery()
my_tesla.fill_gas_tank()
>>>
2018 Tesla Model S
This car has a 70-KWh battery
This car doesn't have a gas tank!
将实例用作属性:
class Car(): --snip-- 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,maker, model, year): """ 初始化父类的属性,再初始化电动车特有的属性 """ super().__init__(maker, model, year) self.battery = Battery() my_tesla = ElectricCar('tesla', 'models s', 2016) print(my_tesla.get_descriptive_name()) my_tesla.battery.describe_battery()
>>>
2016 Teslamiles On It.
This car has a 70 -KWh battery.
3、导入类
我们新建一个文件如:car.py。其中包含了Car类、Battery类、ElectricCar类等若干类。称car.py为一个模块。
导入一个类:from car import ElecticCar
导入多个类:from car import Car , ElectricCar
导入整个模块:import car
导入模块中的而所有类:from module_name import *
在一个模块中导入另一个模块:from module_name import class_name
4、Python 标准库
字典能够将信息关联起来,但是并不记录你添加键-值对的顺序。要创建字典并记录其中的键值对的添加顺序,可使用模块collection中的OrderedDict类。OrderedDict实例的行为几乎与字典相同,区别只在于记录了键值对的添加顺序。
from collections import OrderedDict favorite_languages = OrderedDict()### 记录了键值对的添加顺序 #favorite_languages = {} ###普通情况下。字典时无序的 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 languages is " + language.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.
5、类编码风格:
类名:驼峰法命名法,即将类名中每个单词的首字母全都大写,而不使用下划线。
实例名和模块名都采用小写格式,并在单词间加上下划线。
对于每个类,都应紧跟在类定义后面包含一个文档字符串。简单描述类的功能。
在类中,可使用一个空行来分隔方法;而在模块中可使用两个空行来分隔类。
需要同时导入标准库中的函数和你自己写的函数时,先导入标准库模块的import语句,再添加一个空行,然后编写导入你自己编写的模块的import语句。(可让别人更容易明白程序的哥哥模块来自何方)