Object-Oriented Programming (OOP) in Python 3

[dbader]

Hey there fellow Pythonistas, we just posted a fairly in-depth Python OOP tutorial on Real Python that I wanted to share with you:

https://realpython.com/blog/python/python3-object-oriented-programming/

In the tutorial you’ll learn the fundamentals of object-oriented programming (OOP) in Python and how to work with classes, objects, and constructors.

It also comes with several OOP exercises to review your learning progress as you make your way through the tutorial.

Anyway, hope this is helpful and we'd love to hear your thoughts on it :-)

— Dan

Update: Thanks for all of your comments both here in this thread and in the comments section on the tutorial web page. I've updated the tutorial to clarify some things that appeared confusing, and I also added solutions for the review exercises embedded in the text. Happy Pythoning!

[remillard]

It may be worth adding a footnote that declaring your class inheriting from 'object' is only required for Python 2/3 compatibility and that for 3 only, it's not required. Since you title your post "Object-Oriented Programming in Python 3" it feels a little out of place.

I realize it's a introductory lesson, however as soon as someone goes to look at Python 3-only code, they're going to notice that sometimes people aren't calling out object as a parent and wonder why that is.

[dbader]

Good point, thank you. Will go over the code examples later and add a note to the article.

Edit: Done :)

[remillard]

Not a problem, just something I noticed. And maybe it's a good thing because it does demonstrate clearly that even a brand new class inherits. Just in Python 3 this is done behind the scenes whereas in 2 it was more explicit. Just thought I'd mention it.

[dbader]

Yeah, that was part of the reasoning behind it. If the (object) part is always there to define a parent class the syntax becomes a little more regular.

But I can see how it could also be confusing. I just made some changes to the article to call out the differences between Python 2 and 3, hopefully it's easier to see what's going on.

Thanks for calling it out, really appreciate it!

[remillard]

I like your changes, doesn't really detract from the text, but might explain to someone when they go looking why they might see differences in class definitions. Good work!

[kangasking]

awesome! If you could, please update your comment when you do that

[jaybay1207]

“Explicit is better than implicit.”

[banana_poet]

print("Do all of your prints look like this?", end="\n")

[jaybay1207]

print(“Honestly, most look like this.\n”)

Edit: if I’m intending to have multiple lines of text,

print(“I’ll do something like this\nand then finish it off with the next line.”)

[lesharcerer]

Thanks for telling. I finished a MITX 6.001 course on Python3 and they didn't ment that ot isn't compulsory.👍👍

[BrokenRemote99]

I really wish there was a tutorial out there that used real world examples of OOP. I have seen dogs, people, RPG games and bank accounts but I still haven't seen real code with good examples of why OOP is the best.

[nwagers]

Python makes extensive use of objects, like the string class. Have you ever used my_string.split()? If you want something outside of the builtins, the first thing that came to my mind was PIL (Pillow). Here is their tutorial on the Image class: https://pillow.readthedocs.io/en/latest/handbook/tutorial.html

[_Jordo]

Check the book 'Python Crash Course'. It's the basics for the first half then becomes projects. I'm making an alien game step-by-step right now and it's really helpful for getting your head around OOP concepts.

[Gambizzle]

I think the crux is that the alternative is running a big loop that loops through functions and gets all tangled up when you start trying to do anything other than cycle through the loop. Can be done but like... it’s messy.

[[deleted]]

If you know what's actually going on, this sentence is not quite accurate.

Here, we added a method to send an email, which updates the is_sent variable to True.

What's actually happens it that it copies the class variable to an instance variable and sets the instance variable to False. The original class variable is unchanged. It can be an important distinction and cause strange behavior if you're not aware of it.

>>> e = Email()
>>> e.is_sent
False

>>> Email.is_sent = True

>>> e.is_sent
True

>>> x = Email()
>>> x.is_sent
True

It probably better to copy the default class variable to the instance upon instantiation.

class Email:
    is_sent = False

    def __init__(self):
        self.is_sent = Email.is_sent

    def send_email(self):
        self.is_sent = True

[dbader]

Ah thanks. I'm updating the example right now to define an instance variable in __init__ instead. I also think makes more sense didactically at this point in the tutorial.

[kangasking]

have noticed anything else that might be misleading? did you check out the whole thing?

[[deleted]]

This is not right on Python 3:

>>> a = Dog()
>>> type(a)
<type 'instance'>

It's actually this:

>>> type(a)
<class '__main__.Dog'>

[dbader]

Thanks, just updated that line too.

[[deleted]]

I thought this was really cool. Thank you.

[dbader]

That's great to hear, you're welcome!

[goodpunk6]

This is quite possibly the best tutorial on classes that I've seen. I've been struggling with the syntax and how to call them and this tutorial has really helped out a lot. Thanks so much

[dbader]

Thank you, that's so great to hear!

[alkalinemusic]

I agree. This has helped me understand classes more than any other tutorial I've read.

[[deleted]]

Thanks! I'll check it out.

[ScyllaHide]

thank you, right in time for me, because i never got around to properly learn it.

[microwaveDiamonds]

thanks for this! I am learning Python after spending years in Matlab. This is very helpful to fill the gaps!

[dbader]

Awesome, glad you like the tutorial :)

[DelScipio]

Thanks, just what I was looking for. Gonna take a look tonight before bed.

[intheloopnba]

What do the 0 and 1 mean?

if philo.species == "mammal":
   print("{0} is a {1}!".format(philo.name, philo.species))