在Python中创建一个Dog类

Question

这是我第一次使用python编程，我目前正在研究如何创建一个类。下面是我的代码：

class Dog():#Defining the class 
    """A simple attempt to model a dog."""#Doc string describing the class 

    def _init_(self, name, age):#Special method that Python runs automatically when a new instance is created. 
          #Self must be the first variable in this function 
     """Initialize name and age attributes.""" 
     self.name = name 
     self.age = age 

    def sit(self): 
     """Simulate a dog sitting in response to a command.""" 
     print(self.name.title() + " is now sitting.") 

    def roll_over(self): 
     """Simulate rolling over in response to a command.""" 
     print(self.name.title() + " rolled over!") 

my_dog = dog('willie', 6)#Telling python to create the dog named willie who is 6. 

print("My dog's name is " + my_dog.name.title() + ".")#Accessing the value of the variable created 
print("My dog is " + str(my_dog.age) + " years old.")#Accessing the value of the 2nd variable 

不过，我得到试图建立，指出时的错误消息：

Traceback (most recent call last): 
File "dog.py", line 19, in <module> 
    my_dog = dog('willie', 6)#Telling python to create the dog named willie who is 6. 
NameError: name 'dog' is not defined 

任何想法？构造一个实例时

class Dog: 
    'A simple dog model.' 

    def __init__(self, name, age): 
     'Construct name and age attributes for an instance of Dog' 
     self.name = name.title() 
     self.age = age 

    def sit(self): 
     'Simulate a dog sitting in response to a command.' 
     print(self.name + " is now sitting.") 

    def roll_over(self): 
     'Simulate rolling over in response to a command.' 
     print(self.name + " rolled over!") 

my_dog = Dog(name='willie', age=6) 

print("My dog's name is " + my_dog.name + ".") 
print("My dog is " + str(my_dog.age) + " years old.") 

标题情况下，一次名：

Answer 1

这是一个改进版本。这是“不要重复自己”的例子，也就是DRY原则。