Support transparent empty sequence structuring when None is present

[python-attrs]

Support transparent empty sequence structuring when None is present

[Tinche]

So first of all, apologies for taking almost 5 years to respond. Must have slipped my radar somehow ;)

I don't think I'd like this in cattrs proper since it feels like a niche case. Just out of curiosity, I tried implementing this to see how difficult it'd actually be.

Here's my solution:

from typing import get_origin

from cattrs import Converter

c = Converter()

c.register_structure_hook_func(
    lambda t: get_origin(t) is list, lambda v, t: c._structure_list(v, t) if v else []
)

print(c.structure(None, list[str]))
print(c.structure([1, 2], list[str]))

Maybe not as easy as I'd like, but also not super hard.