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106 lines
2.8 KiB
106 lines
2.8 KiB
10 months ago
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from __future__ import annotations
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import typing as t
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from weakref import ref
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from blinker._saferef import BoundMethodWeakref
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IdentityType = t.Union[t.Tuple[int, int], str, int]
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class _symbol:
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def __init__(self, name):
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"""Construct a new named symbol."""
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self.__name__ = self.name = name
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def __reduce__(self):
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return symbol, (self.name,)
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def __repr__(self):
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return self.name
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_symbol.__name__ = "symbol"
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class symbol:
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"""A constant symbol.
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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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A slight refinement of the MAGICCOOKIE=object() pattern. The primary
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advantage of symbol() is its repr(). They are also singletons.
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Repeated calls of symbol('name') will all return the same instance.
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"""
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symbols = {} # type: ignore[var-annotated]
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def __new__(cls, name):
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try:
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return cls.symbols[name]
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except KeyError:
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return cls.symbols.setdefault(name, _symbol(name))
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def hashable_identity(obj: object) -> IdentityType:
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if hasattr(obj, "__func__"):
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return (id(obj.__func__), id(obj.__self__)) # type: ignore[attr-defined]
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elif hasattr(obj, "im_func"):
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return (id(obj.im_func), id(obj.im_self)) # type: ignore[attr-defined]
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elif isinstance(obj, (int, str)):
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return obj
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else:
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return id(obj)
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WeakTypes = (ref, BoundMethodWeakref)
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class annotatable_weakref(ref):
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"""A weakref.ref that supports custom instance attributes."""
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receiver_id: t.Optional[IdentityType]
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sender_id: t.Optional[IdentityType]
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def reference( # type: ignore[no-untyped-def]
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object, callback=None, **annotations
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) -> annotatable_weakref:
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"""Return an annotated weak ref."""
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if callable(object):
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weak = callable_reference(object, callback)
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else:
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weak = annotatable_weakref(object, callback)
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for key, value in annotations.items():
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setattr(weak, key, value)
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return weak # type: ignore[no-any-return]
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def callable_reference(object, callback=None):
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"""Return an annotated weak ref, supporting bound instance methods."""
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if hasattr(object, "im_self") and object.im_self is not None:
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return BoundMethodWeakref(target=object, on_delete=callback)
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elif hasattr(object, "__self__") and object.__self__ is not None:
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return BoundMethodWeakref(target=object, on_delete=callback)
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return annotatable_weakref(object, callback)
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class lazy_property:
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"""A @property that is only evaluated once."""
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def __init__(self, deferred):
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self._deferred = deferred
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self.__doc__ = deferred.__doc__
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def __get__(self, obj, cls):
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if obj is None:
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return self
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value = self._deferred(obj)
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setattr(obj, self._deferred.__name__, value)
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return value
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