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Object-Oriented Python

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What Are Objects And Classes?

2:45 with Kenneth Love

There are a lot of pieces to Python's object-oriented programming features. Let's talk about them so we can have a shared vocabulary for the rest of the course.

The class keyword lets us define a class. We use it just like we do the def keyword for making functions. Class definitions are blocks like function definitions.

class NewClass:

Inside of the class, variables are called attributes.

class NewClass:
    name_attribute = "Kenneth"

And functions that are defined inside of a class are called methods.

class NewClass:
    name_attribute = "Kenneth"

    def name_method(self):
        return self.name_attribute

Whenever we call a class, it creates an instance. Each instance has full access to the all of the attributes and methods of the class.

new_instance = NewClass()
new_instance.name_method()

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    [SOUND] [SOUND] Hey everyone. 0:00
    I'm Kenneth, the Python teacher here at Treehouse. 0:05
    In this course I'm gonna introduce you to one of the most powerful 0:07
    features of Python. 0:10
    But like many things that give you great power, 0:11
    this one will give you great, no wait, this isn't some comic book. 0:13
    This feature will give you a lot more power and capabilities in you programming. 0:16
    But it won't suddenly make you responsible for the safety of a major city. 0:20
    In the time you spent with Python you probably read or 0:23
    heard that Python is an object oriented programming language. 0:25
    But like so much in the world of programming, 0:28
    that very descriptive name, object oriented programming language, 0:30
    doesn't really mean all that much, does it? 0:33
    Yet more dense programming jargon that we just throw at people. 0:35
    All right, let me break it down a little bit for you. 0:37
    When I was in school and 0:40
    we talked about grammar, nouns were always defined as a person, place, or a thing. 0:41
    And on the surface level, 0:45
    that's a pretty good explanation of an object in programming. 0:46
    If it can be described with adjectives and 0:49
    maybe it can do things with verbs, it's an object. 0:51
    In Python though, everything is an object. 0:54
    When you've used an integer to represent someone's age, you used an int object. 0:56
    When you stored your name in a string, you put your name into an str object. 1:00
    And heck, when you created a function, you actually defined a function object. 1:04
    Most of the time though, we don't need to think about functions being objects. 1:07
    Now, before I get into some terms and definitions, let me say this. 1:11
    Object oriented programming is a major area of programming and program design. 1:15
    You won't understand all of it after doing just this course. 1:19
    I've been using the school of design for over a decade and 1:22
    I keep learning new patterns and approaches to it all the time. 1:24
    So, if at the end of this course you still feel a little fuzzy about it, that's fine. 1:27
    It's to be expected. 1:30
    Just like with any large topic area, like say algebra or baking, you'll have to 1:32
    spend time researching and experimenting with it to really get the most out of it. 1:36
    Okay, let's define a few things and then we'll get into some coding. 1:40
    In Python, object types like int and str and 1:43
    list are defined with a construct known as a class. 1:46
    Instead of using def like in functions, we use the key word class. 1:49
    Nouns have adjectives to describe them. 1:53
    Objects, or classes, have attributes. 1:55
    Attributes are very similar to variables but 1:58
    they're defined inside of a class and belong to that class. 1:59
    And just like nouns can do actions by using verbs, 2:03
    classes have methods to give them special abilities. 2:06
    Methods look just like functions, but again, they belong to the class. 2:08
    When we use a class, 2:12
    like creating a string from a number, we call those resulting object an instance. 2:14
    When that instance is used, like when we change an attribute on it or call 2:18
    a method, the instance is responsible, not the class it was instantiated from. 2:21
    There are actually some other things to consider about attributes and methods, but 2:26
    we’ll dive into them later. 2:29
    Wow, that was a lot to take in and we haven’t even gotten into code yet. 2:30
    You’ll get used to all of this new vocabulary quickly though, 2:33
    because we’ll be using it all through this course. 2:36
    For now, get settled in and read through the teacher’s notes to make sure you’re 2:38
    comfortable with all these new words. 2:41
    There’s a bunch of code and a vocabulary test coming your way. 2:42

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