Scene-Caching w/ "-" as filename bug : Cannot use Updaters.

[Aathish04]

Consider the following test script:

class Test(Scene):
        def construct(self):
                v = ValueTracker(10)
                a = Integer().add_updater(lambda m:m.set_value(v.get_value()))
                self.add(a)
                self.play(v.set_value,100)

Rendering this by saving it as a file, then rendering it will work. However, if you render the same test script by inputting it directly into STDIN, which you can do by providing - as the filename, then the render will fail with the following traceback:

Traceback (most recent call last):
  File "/Users/aathishs/Python/ManimEnv/manim/manim/__main__.py", line 168, in main
    scene = SceneClass()
  File "/Users/aathishs/Python/ManimEnv/manim/manim/scene/scene.py", line 77, in __init__
    self.construct()
  File "<string>", line 7, in construct
  File "/Users/aathishs/Python/ManimEnv/manim/manim/scene/scene.py", line 802, in wrapper
    hash_play = get_hash_from_play_call(
  File "/Users/aathishs/Python/ManimEnv/manim/manim/utils/hashing.py", line 146, in get_hash_from_play_call
    current_mobjects_list_json = [
  File "/Users/aathishs/Python/ManimEnv/manim/manim/utils/hashing.py", line 147, in <listcomp>
    get_json(x) for x in sorted(current_mobjects_list, key=lambda obj: str(obj))
  File "/Users/aathishs/Python/ManimEnv/manim/manim/utils/hashing.py", line 98, in get_json
    return json.dumps(obj, cls=CustomEncoder)
  File "/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/json/__init__.py", line 234, in dumps
    return cls(
  File "/Users/aathishs/Python/ManimEnv/manim/manim/utils/hashing.py", line 82, in encode
    return super().encode(self._encode_dict(obj))
  File "/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/Users/aathishs/Python/ManimEnv/manim/manim/utils/hashing.py", line 40, in default
    return {"code": inspect.getsource(obj), "nonlocals": cvardict}
  File "/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/inspect.py", line 985, in getsource
    lines, lnum = getsourcelines(object)
  File "/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/inspect.py", line 967, in getsourcelines
    lines, lnum = findsource(object)
  File "/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/inspect.py", line 798, in findsource
    raise OSError('could not get source code')
OSError: could not get source code

cc @huguesdevimeux

[huguesdevimeux]

Thanks for the report.

I will add this the stack of 456 things I have to fix of the scene caching.

[Aathish04]

@huguesdevimeux

Come to think of it, the - as filename feature is only used for rapid prototyping, and often only has a single play call. Scene caching would be a hindrance in that case.

I say we disable scene caching internally if - is passed as a filename.

Also, this bug seems to be not due to scene caching itself, but due to the inability of inspect to extract source code from stuff typed into stdin. The same thing happens when using the python shell and trying to get the source code of a prewritten function, so I don't think this is something that can be fixed by refactoring the scene caching mechanism anyway.

[huguesdevimeux]

Yes, I agree.

I say we disable scene caching internally if - is passed as a filenam

Let's do it.

Feel free to PR if you have time, or I will do it in a few days.

[leotrs]

Will #315 close this? @huguesdevimeux said it's about inspect, not scene caching.

If not, let's just document that the - flag does not allow for updaters and close this issue.

[Aathish04]

Will #315 close this? @huguesdevimeux said it's about inspect, not scene caching.

If not, let's just document that the - flag does not allow for updaters and close this issue.

Yup. #315 does fix this. It disables scene caching when - is passed as the filename.

[leotrs]

Ok so let's just document somewhere. I think there should be a whole documentation page on CLI arguments...