Passing datetime args to a function requires unreasonable type wrangling

[anbuzin]

Schema:

module default {
    type Chat {
        content: str;
    }

    function insert_summary(chat_id: uuid, some_date: datetime) -> Chat 
    using (
        with
            chat := (select Chat filter .id = chat_id)
        select assert_exists(chat)
    );
}

Python:

from models import default, std
import gel
import asyncio
import uuid
import datetime


client = gel.create_async_client()


async def main():
    q = default.insert_summary(
        chat_id=std.uuid(uuid.UUID("628612c0-4cf6-11f0-bb23-c7e1e2da40cb")),
        some_date=std.datetime(
            datetime.datetime(2025, 6, 19, 11, 5, 17).replace(
                tzinfo=datetime.timezone.utc
            )
        ),
    )
    result = await client.query(q)


if __name__ == "__main__":
    asyncio.run(main())

This is the minimum possible variant that the QB agreed to work with, and I got a spasm in my scapula while trying to work it out in the context of a FastAPI app that's doing automagic parsing/casting.

The kinds of errors I've encountered:

# no timezone info
gel.errors.InvalidValueError: invalid input syntax for type std::datetime: '2025-06-19 11:05:17'

class SummarizeRequest(BaseModel):
    cutoff: datetime

# ...

cutoff = std.datetime(request.cutoff)
# TypeError: str cannot be converted to an Expr

# when passing raw Python datetime as an arg
TypeError: datetime.datetime cannot be converted to an Expr

UUIDs are no better, but at least they are easier to get right. Could we please make the errors more descriptive?