Python version deprecation tracking

[MarkZH]

This issue is for discussing the scheduling and motivations for deprecating old Python versions.

Deprecating 3.8 (May 1, 2023)

• 685

• [x] Finish type hinting with Queue.
• [x] Use builtin types for hinting (list and dict instead of List and Dict, for example) to reduce the occurrences of from typing import ....

Deprecating 3.9 (Oct. 2025)

• [x] In timer.py, replace time.time() with time.monotonic() so timing is not affected by clock changes (DST, e.g.). This function is available on MacOS starting with version 3.10. Fixed with PR #801
• [ ] Use int | str instead of Union[int, str], and int | None instead of Optional[int].
• [ ] Use TypeAlias, for example: MOVE = Union[PlayResult, list[Move]] changes to MOVE: TypeAlias = Union[PlayResult, list[Move]].
• [ ] Replace long chains of if-elif-else with match statements
• [ ] Remove 3.9 specific instructions from installation wiki.

Deprecating 3.10 (Oct. 2026)

• [ ] Use NotRequired and Required in TypedDicts.

Deprecating 3.11 (Oct. 2027)

• [ ] Use type instead of TypeAlias, to change MOVE: TypeAlias = Union[PlayResult, list[Move]] to type MOVE = Union[PlayResult, list[Move]].
• [ ] Change nested f-strings to only use double quotes (see here).

Deprecating 3.12 (Oct. 2028)

• [ ] Use ReadOnly in TypedDict
• [ ] Possibly support iOS and android.

Deprecating 3.13 (Oct. 2029)

• [ ] Remove some (possibly all) from future import annotations statements.

[AttackingOrDefending]

With deprecating 3.8, we can use list[dict[str, int]] instead of List[Dict[str, int]], so we can remove from typing import List. With deprecating 3.9, we can use int | str instaed of Union[int, str], and int | None instead of Optional[int].

[MarkZH]

With respect to time.monotonic(), I misinterpreted the Python docs. The documentation states that

Changed in version 3.10: On macOS, the function is now system-wide.

I had thought this meant that the function wasn't guaranteed to be available on macOS. However, according to this cpython issue, the definition of "system-wide" is

[...] the clock is the same for all processes on the system and the reference point does not change after start-up time.

Meaning, time.monotonic() is available for macOS, but the timers on different processes cannot be used together until 3.10. Since all of the timers used in lichess-bot never leave their originating thread or process, this limitation is irrelevant.

However, time.monotonic() has much lower time resolution than time.perf_counter(), so the issue is moot and perf_counter() is a better choice for timing purposes.

[AttackingOrDefending]

With deprecating 3.9 we can use TypeAlias, so we would change MOVE = Union[PlayResult, list[Move]] to MOVE: TypeAlias = Union[PlayResult, list[Move]].

With deprecating 3.10 we can use NotRequired and Required in TypedDicts.

With deprecating 3.11 we can use type instead of TypeAlias, so we would change MOVE: TypeAlias = Union[PlayResult, list[Move]] to type MOVE = Union[PlayResult, list[Move]]. We could also change nested f-strings to only use double quotes (see here).

[MarkZH]

@AttackingOrDefending Since Python 3.9 is a little more than a year away from end-of-life, should we deprecate it soon (with, say, 3 months warning) or wait until it reaches end-of-life?

[AttackingOrDefending]

I think we should wait until it reaches end-of-life, since there are probably people still using python 3.9.

[AttackingOrDefending]

With python 3.13 (deprecating 3.12), we can use ReadOnly in TypedDict and also possibly support iOS and android. With python 3.14 (deprecating 3.13), we can remove some (possibly all) from __future__ import annotations statements.