4.4. Creating and Using a Class
You can model almost anything using classes. Let's start by writing a simple class, Dog, that represents a dog (it can be any dog).
You can model almost anything using classes. Let's start by writing a simple class, Dog, that represents a dog (it can be any dog).
Every instance created form the Dog class will store a name and an age, and we'll give each dog the ability to sit() and roll_over() later on.
In the first line, we define a class called Dog. (In Python, class starts with capital letter). In the second line, we write a docstring describing what this class does.
The __init__() method is a special method that Python runs automatically whenever we create a new instance based on the Dog class. We define that method to have three parameters: self, name, and age. The self parameter is a must, and it has to come first before the other parameters.
When we make an instance of Dog, Python will call the __init__() method. We'll pass Dog() a name and an age as arguments; self is passed automatically, so we don't need to pass it. See the example.
The two variables defined in def each have the prefix self. Any variable prefixed with self is available to every method in the class. The line self.name = name takes the value associated with the parameter name and assigns it to the variable name. (Same process with self.age = age). Variables that are accessible through instances like this are called attributes.
The class Dog is a set of instructions that tells Python how to make individual instances representing specific dogs. Let's make an instance representing dog.
To access the attributes of an instance, you use dot notation. This syntax demonstrates how Python finds an attribute's value. Here, Python looks at the instance my_dog and then finds the attribute name and age associated with my_dog.
After we create an instance from the class Dog, we can use dot notation to call any method defined in Dog. Let's make our dog sit and roll over.
We define other two methods: sit() and roll_over(). Because these methods don't need additional information to run, we just define them to have one parameter, self. For now, they simply print a message saying the dog is sitting or rolling over.
You can create as many instances from a class as you need. Let's create a second dog called your_dog:
Restaurant
Make a class called Restaurant. The __init__() method for Restaurant should store two attributes: a restaurant_name and a cuisine_type. Make a method called describe_restaurant() that prints these two pieces of information, and a method called open_restaurant() that prints a message indicating that the restaurant is open.
Make an instance called restaurant from your class. Print the two attributes individually, and then call both methods.
Three Restaurants
Start with your class from no.1. Create three different instances from the class, and call describe_restaurant() for each instance.
Users
Make a class called User. Create two attributes called first_name and last_name, and then create several other attributes that are typically stored in a user profile. Make a method called describe_user() that prints a summary of the user's information. Make another method called greet_user() that prints a personalized greeting to the user.
Create several instances representing different users, and call both methods for each user.