65 lines
1.6 KiB
Python
65 lines
1.6 KiB
Python
from __future__ import annotations
|
|
|
|
import collections.abc as c
|
|
import inspect
|
|
import typing as t
|
|
from weakref import ref
|
|
from weakref import WeakMethod
|
|
|
|
T = t.TypeVar("T")
|
|
|
|
|
|
class Symbol:
|
|
"""A constant symbol, nicer than ``object()``. Repeated calls return the
|
|
same instance.
|
|
|
|
>>> Symbol('foo') is Symbol('foo')
|
|
True
|
|
>>> Symbol('foo')
|
|
foo
|
|
"""
|
|
|
|
symbols: t.ClassVar[dict[str, Symbol]] = {}
|
|
|
|
def __new__(cls, name: str) -> Symbol:
|
|
if name in cls.symbols:
|
|
return cls.symbols[name]
|
|
|
|
obj = super().__new__(cls)
|
|
cls.symbols[name] = obj
|
|
return obj
|
|
|
|
def __init__(self, name: str) -> None:
|
|
self.name = name
|
|
|
|
def __repr__(self) -> str:
|
|
return self.name
|
|
|
|
def __getnewargs__(self) -> tuple[t.Any, ...]:
|
|
return (self.name,)
|
|
|
|
|
|
def make_id(obj: object) -> c.Hashable:
|
|
"""Get a stable identifier for a receiver or sender, to be used as a dict
|
|
key or in a set.
|
|
"""
|
|
if inspect.ismethod(obj):
|
|
# The id of a bound method is not stable, but the id of the unbound
|
|
# function and instance are.
|
|
return id(obj.__func__), id(obj.__self__)
|
|
|
|
if isinstance(obj, (str, int)):
|
|
# Instances with the same value always compare equal and have the same
|
|
# hash, even if the id may change.
|
|
return obj
|
|
|
|
# Assume other types are not hashable but will always be the same instance.
|
|
return id(obj)
|
|
|
|
|
|
def make_ref(obj: T, callback: c.Callable[[ref[T]], None] | None = None) -> ref[T]:
|
|
if inspect.ismethod(obj):
|
|
return WeakMethod(obj, callback) # type: ignore[arg-type, return-value]
|
|
|
|
return ref(obj, callback)
|