These days I am in the process of understanding classes.

The last two days I did this Banking System exercise where I had class Bank and class Account and people could deposit and withdraw money etc.

I was able to make this work but I used way too much ChatGPT and still don’t feel comfortable about the basics, so today I asked ChatGPT for a really simple exercise on classes.

Next is what I got, and you can find my solution below

Exercise: Create a Simple Dog Class

Objective:

• Understand the basic structure of a Python class.

• Learn how to create an instance (object) of a class.

• Get familiar with the concept of methods and attributes.

Task Description:

1. Define a Class:

   • Create a class named Dog.

   • The class should have an __init__ method (constructor) that takes two parameters: name and age.

2. Add Attributes:

   • Inside the __init__ method, assign these parameters to instance attributes called name and age.

3. Create an Instance Method:

   • Add a method named bark to the Dog class.

   • This method doesn't take any parameters besides self.

   • When called, it should print a string: "Woof! My name is [name]!", where [name] is the name of the dog.

4. Create an Instance of the Dog Class:

   • Outside the class, create an instance of Dog. For example, my_dog = Dog("Rex", 5).

   • Print out the name and age of my_dog using the attributes.

   • Call the bark method on your my_dog instance.

My Code

Ok this is perhaps as simple as it gets with classes:

class Dog: # This is the class
    ...

def main():
    dog = Dog # This is an object (as in object-oriented programming)
    dog.name = "Sausage"
    dog.age = 1
    print(f'my dog is called {dog.name} and is {dog.age} years old')

if __name__ == '__main__':
    main()

Next I tried a different way to create the dog object, but this results in an error: TypeError: Dog() takes no arguments

# This Code doesn't work

class Dog: 
    ...

def main():
    name = "Sausage"
    age = 1
    dog = Dog(name, age)
    print(f'my dog is called {dog.name} and is {dog.age} years old')

if __name__ == '__main__':
    main()

Next I added the __init__ method, which nicely makes my code work again

class Dog: 
    def __init__(self, name, age):
        self.name = name
        self.age = age

def main():
    name = "Sausage"
    age = 1
    dog = Dog(name, age)
    print(f'my dog is called {dog.name} and is {dog.age} years old')

if __name__ == '__main__':
    main()

I can still add more attributes that I didn’t define in __init__

class Dog: 
    def __init__(self, name, age):
        self.name = name
        self.age = age

def main():
    name = "Sausage"
    age = 1
    dog = Dog(name, age)
    dog.friend = "Mike"
    print(f'my dog is called {dog.name} and is {dog.age} years old. His friend is {dog.friend}')

if __name__ == '__main__':
    main()

Next I tried to get my dog to bank. The code from my first attempt actually doesn’t do anything, not even create an error

# This Code doesn't work

class Dog: 
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark():
        print(f'Woof! My name is {name}!')

def main():
    name = "Sausage"
    age = 1
    dog = Dog(name, age)
    dog.bark

if __name__ == '__main__':
    main()

Ok turns out I need to call the method with dog.barg() just like a function. Also had to add ‘self’ to the method to make it work with the name.

class Dog: 
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark(self):
        print(f'Woof! My name is {self.name}!')

def main():
    name = 'Sausage'
    age = 1
    dog = Dog(name, age)
    dog.bark()

if __name__ == '__main__':
    main()

Alright that’s it! And now I can create as many dogs as I want and have them bark.

class Dog: 
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark(self):
        print(f'Woof! My name is {self.name}!')

def main():
    name1 = 'Sausage'
    age1 = 1
    dog1 = Dog(name1, age1)

    name2 = 'Rex'
    age2 = 5
    dog2 = Dog(name2, age2)

    dog1.bark() 
    dog2.bark()

if __name__ == '__main__':
    main()

Wow you might think that was way too simple, but it was exactly what I had to get more comfortable with, so very happy with this small dog exercise today. I didn’t use any ChatGPT for help here, but rewatched parts of CS50 Python Week 8 on OOP