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)

• Drop support for Python 3.8 #685
• Finish type hinting with Queue.
• 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 (TBD / EOL: Oct. 2025)

• 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 Replace ints and floats with datetime.timedeltas #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 (TBD / EOL: Oct. 2026)

• Use NotRequired and Required in TypedDicts.

Deprecating 3.11 (TBD / EOL: Occt. 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).

[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).