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Class Concepts: Object-Oriented Programming in Python (Summary)

Christopher Trudeau

Class Concepts: Object-Oriented Programming in Python
Christopher Trudeau 04:34

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Object-oriented programming means that you’re structuring data and operations on that data together. In Python, you accomplish this by building classes with the class keyword. Attributes are the data values, and methods are the function-like operations that you can perform on classes. In this course, you got a taste of writing code using class and its associated attributes and methods.

In this video course, you’ve learned about:

  • The advantages of object-oriented programming
  • Classes, including how to write them
  • Attributes and methods
  • The descriptor protocol

Now that you know how to write and use classes, you might wonder what else you can do with them. This course is part of a three-part series. Part two covers how to write reusable hierarchies of classes using inheritance, while part three dives deeper into the philosophy behind writing good object-oriented code.

If you’re looking to continue your learning journey, then Real Python’s Object-Oriented Programming (OOP) With Python learning path is for you. Additionally, you can check out the following resources:

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Sample Code (.zip)

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Course Slides (.pdf)

1013.9 KB

00:00 In the previous lesson, I showed you all of the things you’ve learned so far in one coding example. This lesson wraps up part one of the course and summarizes what you’ve learned.

00:11 A structure that contains data and operations in Python is defined using the class keyword. And once you have a class, you instantiate it to create an instance of the class called an object.

00:23 Each object has its own attributes and a reference to each method defined in the class. The first method you learned about was the special one known as .__init__().

00:33 This method is called after the object is created and is used to initialize its contents. For most classes, you’ll override the .__init__() method for your own purposes.

00:44 Like all methods, the first argument to .__init__() is self, which when the method is called contains a reference to the newly constructed object.

00:53 You can assign attributes to the object using dot notation. When you do this in .__init__() or any other method, you access the object instance through the self argument. For example, inside Car’s .__init__() method, using self.speed = 3 assigns the value 3 to the attribute named .speed on the instance object.

01:18 An instance object has its own copy of the attributes. When you’re using the object from the outside, you use dot notation on the object to get at its attributes. Within an object’s method, you do the same thing with the object reference called self passed into each method. Attributes can also be at the class level.

01:38 These kinds of attributes are readable by all objects of that class. When you change a class attribute, all objects see the new value. Methods are a special kind of function associated with a class and its objects.

01:53 Instance methods are at the object level and require at least one argument named self, which is the reference of the calling object. Class methods are at the class level.

02:04 They have no knowledge of a specific object. You declare a method as a class method by wrapping it in the @classmethod decorator, and similar to the instance method, they also take at least one argument. In this case, it’s a reference to the class. Class methods are frequently used for factories, an alternative way of creating object instances.

02:26 The third type of method is a static method. These aren’t used very frequently in Python, and they require neither a class nor an object reference. To declare a static method, you wrap it in the @staticmethod decorator.

02:41 The descriptor protocol defines an interface that Python uses to create attribute-like behavior using methods. This gives you fine-grain control over how that thing that looks like an attribute actually behaves under the covers.

02:56 You turn a method into a property by wrapping it with the @property decorator. From the outside, it can be read like an attribute—i.e., without parentheses.

03:06 The user doesn’t need to be aware that this triggers an underlying method

03:11 Associated with the property is the @.setter decorator. This allows you to create a method that is called when you attempt to set the value of a property. Together, the property and setters are like getter and setters in other programming languages, except they hide away the corresponding methods, allowing the user to simply use the property like an attribute.

03:32 The descriptor protocol actually goes even deeper than this, but that will be covered in part two of the course. Speaking of part two, here’s a quick version of what you can look forward to. So far, you’ve been using the attributes and methods on a class, but classes have other features as well.

03:49 You can declare a class using another class in its definition. This is called inheritance and is a way of reusing the functionality of another class while augmenting it and not having to rewrite the code.

04:01 Inheritance can be multilevel: a class can inherit from a class, which inherits from a class, and so on. It can also inherit from multiple classes at the same level.

04:14 All together, these mechanisms provide a good way of writing reusable code. It also allows you to define hierarchical data structures that better map your data to how things appear in the real world.

04:28 That’s it for part one. I hope you found it informative. See you in part two.

mikehillsnc on Sept. 8, 2023

I thought I knew all this basic stuff. However i learned

  • about @property

  • use of dict to define new objects with **kwargs

  • why repl works

Cant wait for parts 2 and 3

thank you

Christopher Trudeau RP Team on Sept. 8, 2023

Glad you found it useful Mike!

pb on Sept. 9, 2023

Thanks! Any ETA on part 2 and 3? :)

Christopher Trudeau RP Team on Sept. 10, 2023

Part 2 should be up in the next couple of days. Part 3 will follow a few weeks after that.

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