Object-oriented Programming In Python Goldwasser Pdf Writer

Object-oriented programming in python goldwasser pdf writer

Watch Now This tutorial has a related video course created by the Real Python team. Object-oriented Programming, or OOP for short, is a programming paradigm which provides a means of structuring programs so that properties and behaviors are bundled into individual objects. For instance, an object could represent a person with a name property, age, address, etc. Or an email with properties like recipient list, subject, body, etc. Put another way, object-oriented programming is an approach for modeling concrete, real-world things like cars as well as relations between things like companies and employees, students and teachers, etc.

OOP models real-world entities as software objects, which have some data associated with them and can perform certain functions.

Object-oriented programming in python goldwasser pdf writer

Another common programming paradigm is procedural programming which structures a program like a recipe in that it provides a set of steps, in the form of functions and code blocks, which flow sequentially in order to complete a task. The key takeaway is that objects are at the center of the object-oriented programming paradigm, not only representing the data, as in procedural programming, but in the overall structure of the program as well.

The primitive data structures available in Python, like numbers, strings, and lists are designed to represent simple things like the cost of something, the name of a poem, and your favorite colors, respectively.

Object-Oriented Programming (OOP) in Python 3

How would you know which element is supposed to be which? What if you had different animals? Are you certain each animal has both a name and an age, and so forth? What if you wanted to add other properties to these animals?

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Classes are used to create new user-defined data structures that contain arbitrary information about something.

In the case of an animal, we could create an Animal class to track properties about the Animal like the name and age.

Object-oriented programming in python goldwasser pdf writer

While the class is the blueprint, an instance is a copy of the class with actual values, literally an object belonging to a specific class. Put another way, a class is like a form or questionnaire.

Object-oriented programming in python goldwasser pdf writer

It defines the needed information. After you fill out the form, your specific copy is an instance of the class; it contains actual information relevant to you. You can fill out multiple copies to create many different instances, but without the form as a guide, you would be lost, not knowing what information is required.

Thus, before you can create individual instances of an object, we must first specify what is needed by defining a class. You start with the class keyword to indicate that you are creating a class, then you add the name of the class using CamelCase notation , starting with a capital letter.

Also, we used the Python keyword pass here. This is very often used as a place holder where code will eventually go. It allows us to run this code without throwing an error.

Python 101: Object Oriented Programming part 1

Note: The above code is correct on Python 3. On Python 2. The object part in parentheses specifies the parent class that you are inheriting from more on this below.

In Python 3 this is no longer necessary because it is the implicit default. All classes create objects, and all objects contain characteristics called attributes referred to as properties in the opening paragraph. This method must have at least one argument as well as the self variable, which refers to the object itself e. In the case of our Dog class, each dog has a specific name and age, which is obviously important to know for when you start actually creating different dogs.

Similarly, the self variable is also an instance of the class. Since instances of a class have varying values we could state Dog. But since not all dogs share the same name, we need to be able to assign different values to different instances. Hence the need for the special self variable, which will help to keep track of individual instances of each class.

While instance attributes are specific to each object, class attributes are the same for all instances—which in this case is all dogs. We started by defining a new Dog class, then created two new dogs, each assigned to different objects.

Object-oriented programming in python goldwasser pdf writer

So, to create an instance of a class, you use the the class name, followed by parentheses. Then to demonstrate that each instance is actually different, we instantiated two more dogs, assigning each to a variable, then tested if those variables are equal.

We created a new instance of the Dog class and assigned it to the variable philo. Using the same Dog class, instantiate three new dogs, each with a different age. Then output the age of the oldest dog like so:. Instance methods are defined inside a class and are used to get the contents of an instance.

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They can also be used to perform operations with the attributes of our objects. In the latter method, speak , we are defining behavior. What other behaviors could you assign to a dog? Look back to the beginning paragraph to see some example behaviors for other objects. Inheritance is the process by which one class takes on the attributes and methods of another. Newly formed classes are called child classes , and the classes that child classes are derived from are called parent classes.

Classes in Python

The most basic type of class is an object , which generally all other classes inherit as their parent. When you define a new class, Python 3 it implicitly uses object as the parent class.

So the following two definitions are equivalent:. Note: In Python 2. There are multiple Dog objects engaging in Dog behaviors, each with different attributes. In regular-speak that means some dogs are running, while some are stretching and some are just watching other dogs.

Furthermore, each dog has been named by its owner and, since each dog is living and breathing, each ages. Each breed of dog has slightly different behaviors. These are child classes of the parent Dog class.

How to write actually object-oriented python - Per Fagrell

The isinstance function is used to determine if an instance is also an instance of a certain parent class. Make sense?

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Both jim and julie are instances of the Dog class, while johnnywalker is not an instance of the Bulldog class. Then as a sanity check, we tested if julie is an instance of jim , which is impossible since jim is an instance of a class rather than a class itself—hence the reason for the TypeError.

Remember that child classes can also override attributes and behaviors from the parent class. For examples:. The SomeBreed class inherits the species from the parent class, while the SomeOtherBreed class overrides the species , setting it to reptile.

Create a Pets class that holds instances of dogs; this class is completely separate from the Dog class. In other words, the Dog class does not inherit from the Pets class. Then assign three dog instances to an instance of the Pets class. Start with the following code below.

Object-oriented programming in python goldwasser pdf writer

Your output should look like this:. The final output should look like this:. Next, add a walk method to both the Pets and Dog classes so that when you call the method on the Pets class, each dog instance assigned to the Pets class will walk.

This is slightly more difficult. Start by implementing the method in the same manner as the speak method. As for the method in the Pets class, you will need to iterate through the list of dogs, then call the method itself. You should now know what classes are, why you would want or need to use them, and how to create both parent and child classes to better structure your programs.

Please be aware that OOP is a programming paradigm and not a Python concept. For further explanation of objected-oriented programming in Python, we recommend that you consult these additional resources:. No spam ever.

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What Is Object-Oriented Programming (OOP)?

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Then output the age of the oldest dog like so: The oldest dog is 7 years old. Your output should look like this: I have 3 dogs. Tom is 6. Fletcher is 7. Larry is 9. And they're all mammals, of course. The final output should look like this: I have 3 dogs. My dogs are not hungry. The output should look like this: Tom is walking! Fletcher is walking!

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