python 快速入門（三）

九. 類

1.創建類

class Dog():
    """一次模擬小狗的簡單嘗試"""

    def __init__(self, name, age):
        """初始化屬性name和age"""
        self.name = name
        self.age = age

    def sit(self):
        """模擬小狗被命令時蹲下"""
        print(self.name.title() + " is now sitting.")

    def roll_over(self):
        """模擬小狗被命令時打滾"""
        print(self.name.title() + " rolled over!")

方法__init__(),類在創建實例時，會自動運行__init__()方法

類中的所有方法參數必須有self，且在其他參數最前面，這樣實例才能夠訪問類中的屬性和方法

2.訪問類屬性

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.調用類方法

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

4.繼承

class Car(object):
    """一次模擬汽車的簡單嘗試"""

    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):
    """電動汽車的獨特之處"""

    def __init__(self, make, model, year):
        """初始化父類的屬性"""
        super(ElectricCar,self).__init__(make, model, year)
        """電動汽車特有屬性"""
        self.battery_size = 70

    """電動汽車特有方法"""
    def describe_battery(self):
        """打印一條描述電瓶容量的消息"""
        print("This car has a " + str(self.battery_size))
    """重寫父類方法"""
    def fill_gas_tank(self):
        print('重寫父類方法')

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
#重寫父類方法

5.導入模塊中的類

創建animal.py文件

class Cat():

    def __init__(self):
        print('創建貓實例')


class Dog():

    def __init__(self):
        print("創建狗實例")
        

創建index.py文件

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

my_dog = Dog()
my_cat = Cat()

十. 文件

1.從文件中讀取數據

創建pi_digits.txt文件

3.1415926535
  8979323846
  2643383279	

創建file_reader.py文件

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

逐行讀取—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. 寫文件，

打開文件時，可指定讀取模式 讀取模式 （‘r’ ）、寫入模式 寫入模式 （‘w’ ）、附加模式 附加模式 （‘a’ ）或讓你能夠讀取和寫入文件的模式（‘r+’ ）。如果你省略了模式實參，Python將以默認的只讀模式打開文件。

filename = 'programming.txt'

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