53 lines
1.1 KiB
Python
53 lines
1.1 KiB
Python
from __future__ import annotations
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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) -> t.Hashable:
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if inspect.ismethod(obj):
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return id(obj.__func__), id(obj.__self__)
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return id(obj)
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def make_ref(obj: T, callback: t.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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