codekingpro/portable-devtools

1from __future__ import annotations2 3import collections.abc as c4import inspect5import typing as t6from weakref import ref7from weakref import WeakMethod8 9T = t.TypeVar("T")10 11 12class Symbol:13    """A constant symbol, nicer than ``object()``. Repeated calls return the14    same instance.15 16    >>> Symbol('foo') is Symbol('foo')17    True18    >>> Symbol('foo')19    foo20    """21 22    symbols: t.ClassVar[dict[str, Symbol]] = {}23 24    def __new__(cls, name: str) -> Symbol:25        if name in cls.symbols:26            return cls.symbols[name]27 28        obj = super().__new__(cls)29        cls.symbols[name] = obj30        return obj31 32    def __init__(self, name: str) -> None:33        self.name = name34 35    def __repr__(self) -> str:36        return self.name37 38    def __getnewargs__(self) -> tuple[t.Any, ...]:39        return (self.name,)40 41 42def make_id(obj: object) -> c.Hashable:43    """Get a stable identifier for a receiver or sender, to be used as a dict44    key or in a set.45    """46    if inspect.ismethod(obj):47        # The id of a bound method is not stable, but the id of the unbound48        # function and instance are.49        return id(obj.__func__), id(obj.__self__)50 51    if isinstance(obj, (str, int)):52        # Instances with the same value always compare equal and have the same53        # hash, even if the id may change.54        return obj55 56    # Assume other types are not hashable but will always be the same instance.57    return id(obj)58 59 60def make_ref(obj: T, callback: c.Callable[[ref[T]], None] | None = None) -> ref[T]:61    if inspect.ismethod(obj):62        return WeakMethod(obj, callback)  # type: ignore[arg-type, return-value]63 64    return ref(obj, callback)65