Pitfall with `prevent_dispatch` arg in `Section` class

While developing using 3.0dev, I misread the documentation and passed in prevent_dispatch=False to allow events to pass to multiple sections. Because of my mistake, I spent 30 minutes trying to figure out why I'm not seeing any events in my other section.

This init code:

arcade/arcade/sections.py

Line 99 in 9aa8e1a

self.prevent_dispatch: Iterable = prevent_dispatch or {True}

Means that if the caller passes in False, it silently gets translates to {true}, which is not intuitive.

I realize this is documented and also that mypy would have caught it, but I fell for it so others probably would too. Since 3.0 is still in beta there's still the possibility of changing the API so I thought I might as well raise this point.

To me, It also seems natural for ''True|False" values to do what you'd expect, but I understand typing simplicity makes this less attractive.

Possible solutions:

1. Use {True} if prevent_dispatch is None else prevent_dispatch instead
2. Add asserts on input types.

[DragonMoffon]

I think this behaviour is just flawed in general thank you for raising the issue. Sections are going to be reworked in a future update (after 3.0) so finding all these hiccups is a huge help. I'm not sure why this wasn't changed when the issue was documented.
I've updated it to use the line you recommended.

if prevent_dispatch=False, then prevent_dispatch will remain a bool. Doesn't the downstream code expect it to be an Iterable?

[DragonMoffon]

yeah, you are correct I'm still trying to figure out if there is a way to solve this issue without using an isinstance check. Admittedly this is only in initialization so it might not be that significant.

[alejcas]

Means that if the caller passes in False, it silently gets translates to {true}, which is not intuitive.

Is defined as an Iterable. A bool is not an iterable.

But yes user may expect to pass False or True

[pushfoo]

@AnonymousCoward128746 let us know if the isinstance checks are too slow.

Recap of the thread here + discussion with Dragon on Discord in the 3.0 release thread:

1. If it's only creation-time for the Section it's probably fine
   • isinstance can be slow
   • lots of real-time section creation is not a good idea in general
2. There are optimization tricks we can dust off and try later after 3.0 ships

Thanks @pushfoo. Works for me. 👍