python 快速入门（三）

九. 类

1.创建类

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):
        """模拟小狗被命令时蹲下"""
        print(self.name.title() + " is now sitting.")

    def roll_over(self):
        """模拟小狗被命令时打滚"""
        print(self.name.title() + " rolled over!")

方法init(),类在创建实例时，会自动运行init()方法

类中的所有方法参数必须有self，且在其他参数最前面，这样实例才能够访问类中的属性和方法

2.访问类属性

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's name is Willie.
#My dog is 6years old.

3.调用类方法

my_dog.sit()
my_dog.roll_over()
#Willie is now sitting.
#Willie rolled over!

4.继承

class Car(object):
    """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
        self.odometer_reading = 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.")

    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

    def fill_gas_tank(self):
        print ("This car need a gas tank!")

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"""
        super(ElectricCar,self).__init__(make, model, year)
        """电动汽车特有属性"""
        self.battery_size = 70

    """电动汽车特有方法"""
    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))
    """重写父类方法"""
    def fill_gas_tank(self):
        print('重写父类方法')

my_tesla = ElectricCar('tesla', 'models', 2016 )
print(my_tesla.get_descriptive_name())
my_tesla.describe_battery()
my_tesla.fill_gas_tank()

#2016 Tesla Models
#This car has a 70
#重写父类方法

5.导入模块中的类

创建animal.py文件

class Cat():

    def __init__(self):
        print('创建猫实例')


class Dog():

    def __init__(self):
        print("创建狗实例")
        

创建index.py文件

from animal import Cat,Dog
#或者 from animal import *

my_dog = Dog()
my_cat = Cat()

十. 文件

1.从文件中读取数据

创建pi_digits.txt文件

3.1415926535
  8979323846
  2643383279    

创建file_reader.py文件

with open('pi_digits.txt') as file_object:
    contents = file_object.read()
    print(contents)
#3.1415926535
#  8979323846
#  2643383279   

逐行读取---rstrip 可去除空白行

filename = 'pi_digits.txt'
with open(filename) as file_object:
    for line in file_object:
        print(line.rstrip())
#3.1415926535
#  8979323846
#  2643383279

2. 写文件，

打开文件时，可指定读取模式 读取模式 （'r' ）、写入模式 写入模式 （'w' ）、附加模式 附加模式 （'a' ）或让你能够读取和写入文件的模式（'r+' ）。如果你省略了模式实参，Python将以默认的只读模式打开文件。

filename = 'programming.txt'

with open(filename, 'w') as file_object:
    file_object.write("I love programming.")