Class-Based vs Function-Based Context Managers

Python Context Managers and the "with" Statement Dan Bader 01:33

After writing class-based and function-based context managers, this lesson compares both of them and names certain trade-offs that might occur.

For more information on context managers, check out Context Managers and Python’s with Statement as either a written tutorial or a video course.

Congratulations, you made it to the end of the course! Make it stick: Mentor AI will check what you’ve got down, help you build something with it, and find your #1 takeaway to share in the discussion.

Or go straight to the discussion section and share your #1 takeaway and how you’ll put your new skills to use.

00:00 So, with this technique, using contextlib and using the @contextmanager decorator, you can write some of these context managers a lot quicker.

00:10 I guess the downside is that for someone to understand this piece of code, they would have to have some basic knowledge about decorators and they would also have to have some basic knowledge about how generators work in Python, right? So, when you compare that with the class-based implementation, you could actually say, “Hey, the class-based implementation communicates what’s going on much more clearly for someone who’s not an expert at Python.” So depending, you know, how your team feels about this, and what everyone’s expertise level is, it’s kind of a fine balance with what concepts you want to pull into this.

00:42 Personally, I think this is pretty beautiful, right? This is awesome. This is very Pythonic. But on the other hand, it requires someone to understand many, many more concepts in order to actually understand what’s going on looking at this. I mean, they’re going to still use it the same way, so they might not care, but I just wanted to mention that because, in my mind, code always needs to communicate what’s going on. Code is communication.

01:06 And this is a great example where you can see where the trade-offs are, right? And I can’t make those decisions for you, but it will be something that you need to decide within the context of your team, the project you’re working on, and so on, right?

01:19 I just wanted to mention that. All right, so I hope that gave you a good overview of how these context managers work, how the with statement works behind the scenes, and what you can do with them.

mikesult on March 3, 2020

Nice to get an understanding of the context manager protocol and how some of the dunder methods work. Thank you for another great tutorial.

legendarylisak on March 29, 2020

Great explanation of the generator and contextmanager.

Cristian Palau on April 9, 2020

Very interesting. Thanks Dan!

Liam Pulsifer RP Team on May 5, 2020

Nice work as always, Dan :)

pwells314 on June 14, 2020

Dan,

I understand the “obvious” vs “elegant” argument, but is there any behavioral or performance reason to prefer one approach over the other?

Thanks Paul

Ghani on Oct. 15, 2020

Great course; thanks Dan.

michael on May 29, 2021

Hi Dan,

Many thanks for clear explanation. I understand that the with statement simplifies exception handling. But if an error occurs, what is the typical pattern for dealing with them (e.g. in database connections)? Put the with-statement in an additional try-except clause?

Bartosz Zaczyński RP Team on May 31, 2021

@michael That’s correct. The most common way to handle exceptions raised in a with clause would be to wrap the entire clause in another try..except clause:

try:
    with open(path) as file:
        pass  # Raise exception
except SomeException as ex:
    pass  # Handle the exception

Pavneet Ghai on May 23, 2022

I wish we had example on SQLite db.

Martin Breuss RP Team on May 23, 2022

@Pavneet Ghai what are you looking for regarding SQLite? Did you check out some the tutorials we have on it:

Become a Member to join the conversation.