Why get_cog is annotated to return Optional[Cog]?

[Aman-14]

Get cog is annotated to return Optional[Cog] but it returns a subclass of Cog.

Adding get_cog in my bot class with bound return type solved this problem, just wanted to know why its annotated that way.

[Rapptz]

The internal mapping is stored as Dict[str, Cog]. Therefore get_cog returns Optional[Cog]. Your suggestion of doing Optional[CogT] would mean that the mapping would have to be Dict[str, CogT] and this generic would have to be propagated to the Bot class as a generic. However, it would also mean that rather than just using polymorphism it also uses monomorphism which would make all cogs be a subtype of whatever CogT generic is passed to the bot. When CogT is Cog this is more or less the same thing.

Likewise, if Reminder is a subtype of Cog then you can just downcast it. I suggest getting a different type checker like Pyright which understands code like this.