MyPy missed type error

[CarlBeek]

In #1234 , MyPy missed that the a type was incorrect despite the object being passed to typed functions. Specifically, next_epoch was cast to a Shard type and passed into get_compact_committees_root which is typed to accept an Epoch.

Does anyone know why? (Particularly someone who understands Python typing better than I).

[protolambda]

Currently SSZ is set to coerce any uint input, but only if it's of the same byte length. All for readability and minimal changes (ugly wrapping in Slot/Epoch), as a lot had to be modified at the time of introducing typing.
See https://github.com/ethereum/eth2.0-specs/blob/2e41f2da3b12c7cf056ee7035ec4ec3a3a707ea1/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py#L111 if you like to change it.

[CarlBeek]

I see, that makes a lot of sense. I don't really have an issue with it, I just think it partially defeats the purpose of static typing if we bypass such checks. I will look deeper into this and develop propper feelings one way or another post ❄️❄️❄️.

[JustinDrake]

Closing for now because it isn't super important or actionable. I guess we need to keep this in the back of our mind—feel free to reopen :)