radarsat1

Let's say I have a context manager that provides a resource that then mutates on exit:

from contextlib import contextmanager

@contextmanager
def context():
    x = ['hi']
    yield x
    x[0] = 'there'

I found that if I want to make another context class that uses this, such that the context (before mutation) is valid, I have to pass it in:

class Example1:
    def __init__(self, obj):
        self.obj = obj
    def use_obj(self):
        print(self.obj)
    def __enter__(self):
        print("start")
        return self
    def __exit__(self, *exc):
        print("end")

with context() as x:
    with Example1(x) as y:
        y.use_obj()

prints:

start
['hi']
end

However, what I don't like is, let's say that obj is an internal detail of my class. I don't want the user to have to define it beforehand and pass it in.

The only way I can figure how to do this is by calling the context manager's __enter__() explicitly:

class Example2:
    def use_obj(self):
        print(self.obj)
    def __enter__(self):
        print("start")
        self.ctx = context()
        self.obj = self.ctx.__enter__()
        return self
    def __exit__(self, *exc):
        print("end")
        self.ctx.__exit__(None, None, None)

with Example2() as y:
    y.use_obj()

which also prints,

start
['hi']
end

For comparison, just as some other random attempt, the following doesn't work because the context ends when self.obj is created:

class Example3:
    def use_obj(self):
        print(self.obj)
    def __enter__(self):
        print("start")
        with context() as x:
            self.obj = x
        return self
    def __exit__(self, *exc):
        print("end")

with Example3() as y:
    y.use_obj()

which prints,

start
['there']
end

Okay, so my point is that Example2 is the right solution here. But, it's really ugly. So my question is, is there a better way to write Example2?

An idea that just occurred to me. I was looking for communities on machine learning to join, so I searched https://browse.feddit.de/ and found a bunch. They don't have much content but together they have at least 4 or 5 posts each, which adds up to a few posts, so I subscribed to all of them.

However, now I have no way of "grouping" them so that I can view posts of all communities in my feed related to the topic of machine learning.

I was wondering if some concept of "super communities" could be interesting for Lemmy, similar to "multireddits". People could curate their collection of favourite communities around a topic, over multiple instances, and users could easily subscribe and browse the whole bunch of them.