String type annotations break backwards compatibility

[adebrecht661]

3.2 changed some type annotations to use string annotations instead of types, e.g.

3.1: DictRow: TypeAlias = Dict[str, Any]
3.2: DictRow: TypeAlias = "dict[str, Any]"

This breaks any code using | for type unions with these types (DictRow | tuple, for example), which worked in 3.1 but in 3.2 raises a TypeError: unsupported operand type(s) for |: 'str' and 'type'.

[dvarrazzo]

Thank you for your report. Which Python version are you using?

[adebrecht661]

This is on Python 3.12.4.

[dvarrazzo]

I wonder what is the extent of the problem, and what is that should be fixed.

I don't think we can eliminate string type aliases altogether. Having a check through the codebase, for instance, I don't think we can eliminate:

psycopg/psycopg_pool/psycopg_pool/_acompat.py

Line 33 in bb47d39

AWorker: TypeAlias = "asyncio.Task[None]"

Because asyncio.Task wasn't generic in 3.8 and I don't think there is any friendly alias.

OTOH AWorker is not a public type, never advertised so.

So maybe we can go soft and only address the type that we have somewhat exposed publicly. Off the bat, I would say everything exposed by:

• psycopg
• psycopg.abc
• psycopg.rows
• psycopg_pool
• psycopg_pool.abc

What do you think, @adebrecht661? Which TypeAlias have you found useful to use from psycopg definitions?

@dlax, have you got an opinion about the issue?

Thank you very much.

[adebrecht661]

Looking at the linked PR and the commit history, that seems like a reasonable solution.

[dvarrazzo]

@adebrecht661 as a workaround in order to get unblocked before we make a new release, is the breakage solved if you define your typealias as string as well?

MyType: TypeAlias = "DictRow | tuple"

[adebrecht661]

We've pinned to < 3.2 for now, but I expect that would also work.