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