Add autoreload mechanism

[Splines]

🎈 Motivation

IPython offers an %autoreload all magic command:

autoreload reloads modules automatically before entering the execution of code typed at the IPython prompt.

This makes it possible for Manim users to make changes in imported files and see those changes reflected automatically without having to reload manually (by means of quitting and restarting the terminal, or by means of the new reload() command from #2251). Therefore, this PR improves the interactive experience with Manim fostering playful change of parameters/functions etc.

💻 Proposed changes

• Add a new --autoreload CLI flag.
• If that flag is set, call the respective magic commands before the InteractiveShellEmbed shell is started.

Note that autoreload should probably not be activated by default because it will slow down the performance since modules will be reloaded automatically and maybe even in cases where it wouldn't be necessary. Furthermore, we should be aware of the caveats that come with autoreload. This is why I went for exposing it as flag that can be activated if users like to.

🧪 Test

# file a.py
import sys

sys.path.append(".")
from manimlib import *

from b import B

class AScene(Scene):
    def construct(self):
        ## Starting
        print("Hello from AScene")

        ## B
        b = B()
        print(b.answer_to_life())

# file b.py
class B:
    def answer_to_life(self):
        return 10

# Line 13 is where the comment "## B" is
manimgl "/path/to/a.py" AScene -se 13 --autoreload

• Preview by starting from the second comment (## B) and get 10 printed to the console.
• Change 10 to 42 in b.py and save the file
• Preview again and see 42 in the console, without having to reload manually 🎉

Tip

Unfortunately, classes inside the same file won't be autoreloaded, just modules that are imported. E.g. see the evolute test example provided in #2240. So when defining custom classes that don't just host Manim rendering logic like self.play() etc., it might be worth to outsource such parts to another file when we want to work on them and make lots of changes. Otherwise, starting with #2251, the reload() command such also work in such cases.

If you want to reload classes from other modules, I just found this post.

📜 Documentation

I've added the CLI flag --autoreload to the docs.

I also tried to build the docs but didn't succeed

I wanted to test this by following your instructions from here. Unfortunately, I stumbled into these issues:

Jinja

I first got this error and therefore downgraded Jinja:

$ pip install "jinja2<3.1"

> Successfully uninstalled Jinja2-3.1.4
> Successfully installed jinja2-3.0.3

Sphinx

Then I tried to run make html again which failed with:

WARNING: while setting up extension sphinx.addnodes: node class 'meta' is already registered, its visitors will be overridden

Sphinx version error:
The sphinxcontrib.applehelp extension used by this project needs at least Sphinx v5.0; it therefore cannot be built with this version.

Realizing that Sphinx==3.0.3 is specified in docs/requirements.txt, I quit this pursuit to build the docs as I was not even sure it would work on your end...

[Splines]

Nice, the new scene_embed makes it a lot easier to get a grasp on what is going on! I've now made my PR ready for the new changes. (Also note my review comment here where I describe how tempfile doesn't work for me. Note that GitHub is slow and you have to wait a few seconds after clicking the link...)

[3b1b]

This looks useful. I'm in the midst of refactoring how the global configuration works, which may affect this. I'll probably incorporate the changes here into a new PR once I'm finished.